The Populares emerged as a political group with the reforms of the Gracchi brothers, who were tribunes of the plebs between 133 and 121 BC. Although the Gracchi belonged to the highest Roman aristocracy, being the grandsons of Scipio Africanus, they were concerned for the urban poor, whose dire condition increased the risk of a social crisis at Rome. They tried to implement a vast social program comprising a grain dole, new colonies, and a redistribution of the Ager publicus in order to alleviate their situation. They also drafted laws to grant the Roman citizenship to Italian allies, and reform the judicial system to tackle corruption. Both brothers were nevertheless murdered by their opponents, the Optimates—the conservative faction representing the interests of the landed aristocracy, who dominated the Senate. Several tribunes of the plebs later tried to pass the Gracchi's program by using plebiscites (in order to bypass senatorial opposition), but Saturninus and Clodius Pulcher suffered the same fate as the Gracchi. Furthermore, many politicians of the late Republic postured as Populares to enhance their popularity among the plebs, notably Julius Caesar and Octavian (later Augustus), who finally enacted most of the Populares' platform during their rule.
The Populares counted a number of patricians—the most ancient Roman aristocrats—such as Appius Claudius Pulcher, Lucius Cornelius Cinna, or Julius Caesar. They were allied to politicians of lesser status, especially to "new men" like Gaius Marius, or Gaius Norbanus (who was even perhaps a new Roman citizen).
The plebeian tribunes (the representatives of the plebeians) and the Plebeian Council (the assembly of the plebeians) at times clashed with the Senate over the mentioned reforms and over the power relationship between the plebeian institutions and the Senate. The Optimates among the senators spearheaded the senatorial opposition. These tribunes were supported by Populares politicians such as Gaius Marius and Julius Caesar, who were often patricians, or equites (equestrians, the second social rank in Rome). Their conflicts also played a part in some of the civil wars of the Late Roman Republic: Sulla's first civil war (88–87 BC), Sulla's second civil war (82–81 BC), the Sertorian War (83–72 BC), Lepidus' rebellion (77 BC), Caesar's Civil War (49–45 BC), the post-Caesarian civil war (44–43 BC), the Liberators' civil war (44–42 BC) and the Sicilian revolt (44–36 BC).
The Populares reached the height of their ascendancy four times. The first one was with the Gracchi brothers, who mobilized the plebeians in support of their land reform and their challenge to senatorial supremacy (133 BC and 122 BC). This almost was not the issue because the Populares had help from the Italians and they had to offer more land to the Italians than they wanted to. The land was meant to go to the poor. The second time was with Gaius Marius and his son Gaius Marius the Younger, when the Marians (the supporters of Marius, who were Populares) seized power and held Rome from 87 BC to 82 BC. They were defeated in Sulla's Second Civil War. This was caused by the deteriorating relationship between Sulla and Marius as they started to fall apart from the consul stand point and lost view of what was important. The third time was when Julius Caesar was elected as consul in 59 BC with the support of Marcus Licinius Crassus and Pompey, who formed an informal alliance with Caesar which historians call the First Triumvirate (60–53 BC). These three helped bring Rome back to order from the scene it was when Sulla had left. The First Triumvirate gave each of the men their own land to watch over so parts of Rome were equally distributed among themselves so none of them would have too much to rule over. Caesar managed to pass an agrarian law for a land reform, which had not been achieved since the agrarian law of Tiberius Sempronius Gracchus of 133 BC as all subsequent attempts at agrarian legislation had been thwarted by the opposition and obstructionism of the Optimates. Tensions between Populares and Optimates had increased with the Catiline conspiracy (63 BC) against the consulship of Marcus Tullius Cicero (an Optimate) during which Cicero, supported by a final decree (senatus consultum ultimum) of the Senate, had some of the conspirators executed without trial. There were demonstrations against these summary executions and this display of arbitrary senatorial power. There were two attempts to counter senatorial dominance which failed, but they were popular. The proponents were Quintus Caecilius Metellus Nepos Iunior, a plebeian tribune; and Julius Caesar, who at the time was a praetor. This enhanced Caesar's popularity and was a help for his creation of the First Triumvirate three years later. The fourth time was with Caesar's Civil War, when Caesar held power from 49 BC to when he was assassinated in 44 BC. Caesar relied on the support of the people for his power. After the defeat of Sextus Pompey (the son of Pompey) in the Sicilian Revolt by the Second Triumvirate in 36 BC, the Populares ceased to be a relevant political label.
Notable Populares included men who held the plebeian tribunate such as the Gracchi brothers, Gaius Papirius Carbo, Lucius Appuleius Saturninus, Marcus Livius Drusus, Publius Sulpicius Rufus, Servilius Rullus and Publius Clodius Pulcher; and men who held the consulship such as Appius Claudius Pulcher, Publius Mucius Scaevola, Marcus Fulvius Flaccus (who also became a plebeian tribune), Gaius Marius, Gaius Marius the Younger, Lucius Cornelius Cinna, Gnaeus Papirius Carbo, Marcus Aemilius Lepidus and Julius Caesar. There were other notable Populares such as Quintus Sertorius, who participated in the capture of Rome by the Marians in 87 BC and fought the Sertorian War, Marcus Aemilius Lepidus and Marc Antony, who fought for Caesar, were given a consulship by him and later became members of the Second Triumvirate. Although Marcus Licinius Crassus did not play a prominent part in Roman politics apart from his consulship in 70 BC, prior to being part of the First Triumvirate he was known as a supporter of the Populares. Pompey was also a member of the First Triumvirate. The Optimates in the Senate side-lined him and frustrated his attempts to have his settlements in the east after his victory in the Third Mithridatic War ratified and to promote an agrarian reform to redistribute land to his veterans. Pompey's attacks pushed back Mithridates and Pompey even managed to get Mithridates's son to become an ally of Rome. As a result, he joined forces with Caesar and Crassus. After the death of Crassus, Pompey drifted towards the Optimates. These shifting allegiances are reminders that the designation Populares refers as much to political tactics as to any perceived policy. Holland notes that republican politicians "had always been more divided on issues of style than of policy".
A historian of the Late Republic cautions against understanding the terms populares and optimates as formally organized factions with an ideological basis:
Our chief contemporary witnesses to the political life of the late Republic, Cicero and Sallust, are fond of analyzing the political struggles of the period in terms of a distinction between optimates and populares, often appearing with slight variations in terminology, such as Senate, nobility, or boni versus People or plebs. But what precisely is denoted and connoted by this polarity? Clear enough, one who is designated in these sources as popularis was at least at that moment acting as 'the People's man,' that is a politician — for all practical purposes, a senator — advocating the rights and privileges of the People, implicitly in contrast to the leadership of the Senate; an 'optimate' (optimas), by contrast, was one upholding the special custodial and leadership role of the Senate, implicitly against the efforts of some popularis or other. The polarity obviously corresponds with the dual sources of institutional power in the Republic — Senate and People — and was realized in practice through contrasting political methods [...] and distinctive types of rhetorico-ideological appeals suited to tapping those alternative sources of power [...]. It is important to realize that references to populares in the plural do not imply a co-ordinated 'party' with a distinctive ideological character, a kind of political grouping for which there is no evidence in Rome, but simply allude to a recognizable, if statistically quite rare, type of senator whose activities are scattered sporadically across late-Republic history[.] [...] The 'life-long' popularis [...] was a new and worrying phenomenon at the time of Julius Caesar's consulship of 59: an underlying reason why the man inspired such profound fears.
This summarizes the dominant interpretation of the Populares in 20th-century scholarship, deriving in large part from Ronald Syme in the Anglophone literature. In the early 21st century and as early as the publication of the ninth volume of The Cambridge Ancient History in 1994, the validity of examining Popularist ideology in the context of Roman political philosophy has been reasserted. In particular, T. P. Wiseman has rehabilitated the use of the word "party" to describe the political opposition between Optimates and Populares, based on Latin usage (partes) and pointing to the consistency of a sort of party platform based on the food supply and general welfare of the populus ("people"), making land available to those outside the senatorial elite and debt relief.
- de Ligt, Luuk and Northwood, Simon J. People, Land, and Politics: Demographic Developments and the Transformation of Roman Italy 300 BC-AD 14 (2008). Leiden. Brill NV.
- Santangelo, Federico. Sulla, the Elites and the Empire a Study of Roman Policies in Italy and the Greek east. Brill Leiden. pp. 18–23.
- Sheppard, P. (producer). (2010). Rome: Part Two: From the Late Republic to the Fall of the Roman Empire: 121 BC to 476 AD (2010, audio video file). Phil Sheppard Productions. Retrieved from World History in video database.
- Sumner, G. V. Cicero, Pompeius, and Rullus (1966). Transactions and proceedings of the American Philological Association. Vol. 97. pp. 573.
- Mitchell, T. N. Cicero, Pompey and the Rise of the First Triumvirate (1973). Traditio. Vol. 29. pp. 2–8.
- Pelling, Christopher. "Plutarch and Roman Politics" in Past Perspectives: Studies in Greek and Roman Historical Writing. Papers Presented at a Conference in Leeds, 6–8 April 1983 (Cambridge University Press, 1986). pp. 159–16, 165–169.
- Plutarch (Parallel Lives, the Life of Caesar) is very concerned to explain Julius Caesar's rise to tyranny. From the beginning, Caesar is the champion and the favorite of the Roman demos. When they support him, he rises, but when he loses their favor he falls too.
- Cassius Dio (36.43.3) noted that Julius Caesar "courted the good-will of the multitude, observing how much stronger they were than the senate".
- Millar, Fergus. The Crowd in Rome in the Late Republic (University of Michigan Press, 2002). pp. 75–76 et passim.
- Taylor, Lily Ross. Party Politics in the Age of Caesar (University of California Press, 1949). p. 93 et passim.
- Brunt, Peter. The Fall of the Roman Republic and Related Essays (Oxford University Press, 1988). pp. 1–92.
- Yavetz, Zvi. "The Popularity of Julius Caesar" in Plebs and Princeps (Transaction, 1988). pp. 38–57; 45 ("Such was Caesar's policy: consolidation based on a body of supporters as heterogenous in class as possible, among them the plebs urbana").
- Mouritsen, Henrik. Plebs and Politics in the Late Roman Republic (Cambridge University Press, 2001). pp. 1, 9, et passim.
- Baehr, Petter R. Caesar and the Fading of the Roman World: A Study in Republicanism and Caesarism. (Transaction Publishers, 1998).On the paradox of "Caesarism" (i.e. the combination of popular support and tyranny),
- Sumner, G. V. Cicero, Pompeius, and Rullus (1996). Transactions and proceedings of the American Philological Association. Vol. 97. p. 573.
- Mayor, Adrienne. The Poison King : The Life And Legend Of Mithradates, Rome's Deadliest Enemy (2009, e-book). Princeton, New Jersey. Princeton University Press. Available from eBook Collection (EBSCOhost) in Ipswich, Massachusetts. Retrieved 16 November 2017.
- Boatwright, Gargola (2004). p. 244.
- Holland, T. Rubicon: The Last Years of the Roman Republic (2003). London. Abacus. p. 194.
- Robert Morstein-Marx, Mass Oratory and Political Power in the Late Roman Republic (Cambridge University Press, 2003), pp. 204–205.
- Andrew Lintott. "Political History, 146–96 B.C." in The Cambridge Ancient History (Cambridge University Press, 1994). p. 52.
- Though this has been a strand in Wiseman's scholarship over the decades, see particularly the introduction and "Roman History and the Ideological Vacuum" in Remembering the Roman People: Essays on Late-Republican Politics and Literature (Oxford University Press, 2009) at p. 14 for partes and "party". A less truncated version of "Roman History and the Ideological Vacuum" may be found in Classics in Progress (Oxford University Press, 2006), p. 285.
- Brunt, Peter. "The Roman Mob" (1966). Past and Present. Vol. 35. pp. 3–27.
- Holland, Tom. Rubicon: The Last Years of the Roman Republic (2003). London. Abacus.
- Hölkeskamp, Karl-J. "Conquest, Competition and Consensus: Roman Expansion in Italy and the Rise of the nobilitas" (1993). Historia. Vol. 42. pp. 12–39.
- Millar, Fergus. "Politics, Persuasion and the People before the Social War (150–90 B.C.)" (1986). Journal of Roman Studies. Vol. 76. pp. 1–11.
- Millar, Fergus. "Political Power in the Mid-Republic: Curia or Comitium?" (1989). Journal of Roman Studies. Vol. 79. pp. 138–150.
- Millar, Fergus. "Popular Politics at Rome in the Late Republic" (1995). Leaders and Masses in the Roman World: Studies in Honor of Zvi Yavetz. Edited by I. Malkin and Z. W. Rubinsohn. Leiden. E.J. Brill.
- Millar, Fergus. The Crowd in Rome in the Late Republic (2002). University of Michigan Press.
- Parenti, Michael. The Assassination of Julius Caesar: A People's History of Ancient Rome (2003). The New Press. ISBN 1-56584-797-0.
- Seager, Robin. "Cicero and the Word popularis" (1972). Classical Quarterly. Vol. 22. pp. 328–338.
- Sherwin-White, A. N. "The Lex repetundarum and the Political Ideas of Gaius Gracchus" (1982). Journal of Roman Studies. Vol. 72. pp. 18–31.
- Taylor, Lily Ross. Party Politics in the Age of Caesar (1949). Berkeley, California. University of California Press.
- Yakobson, Alexander. "Petitio et largitio: Popular Participation in the Centuriate Assembly of the Late Republic" (1992). Journal of Roman Studies. Vol. 82. pp. 32–52.
- Videos of talks by Michael Parenti about his book The Assassination of Julius Caesar: A People's History of Ancient Rome, which describes the conflict between Optimates and Populares (in a 76 minute talk in one part and in eight parts).