According to Pliny he was born with teeth, thus the cognomen "Dentatus".
He first appears as consul in 290 BC, defeating both the Samnites and Sabines that year, and (according to the sources) celebrating two triumphs. As suffect consul in 284 he defeated the Senones, as consul again in 275 he decisively defeated Pyrrhus in the battle of Beneventum, and the Lucani in the following year. He was censor in 272.
At home Dentatus was responsible for partly draining Lake Velinus (289), and in 272 began the construction of the Anio Vetus, Rome's second aqueduct.
He was supposed to have been incorruptible and frugal; the story was that when the Samnites sent ambassadors with expensive gifts in an attempt to influence him in their favor, they found him sitting by the hearth roasting turnips. He refused the gifts, saying that he preferred ruling the possessors of gold over possessing it himself. Although the truth of this story is unclear - it may have been an invention of Cato - it was the inspiration for a number of paintings, by Jacopo Amigoni, Govert Flinck, and others.
His praenomen is sometimes erroneously given as "Marcus" because the standard abbreviation of Manius, "M'." is easily confused with the "M." abbreviation for "Marcus".