Her father was the son of Marcus Valerius Messala Messallinus and Claudia Marcella Minor, daughter to Gaius Claudius Marcellus and Octavia. Her mother was the granddaughter of Marcus Antonius and Octavia through their daughter Antonia Major. As grandchildren of Octavia, her parents were first cousins. Octavia herself was sister to Caesar Augustus.
Thus Messalina was closely related to the Julio-Claudian dynasty and had been a regular at the court of Caligula.
She married Claudius around 38 and bore him two children, Britannicus (41–55), who might actually have been fathered by Caligula, and Octavia (40–62), who married her own stepbrother, the emperor Nero. In 48, Messalina conspired with Caius Silius to kill Claudius while her husband was in Ostia. She actually went through a public marriage ceremony with Silius (he was already married to Junia Silana). Apparently, she was motivated by the protection the powerful and popular Silius could give her over the weakness of Claudius. Her plotting was sufficiently promising that many senior officials were swayed to her side. However, the plot was exposed by Narcissus, an advisor to Claudius. Messalina, Silius and a number of others were summarily executed. Messalina was apparently offered the opportunity of suicide but was unable to do it.
Her reputation is very poor. A number of Roman historians (mainly Tacitus and Suetonius) portray her as a cruel, avaricious, foolish nymphomaniac who had many wild affairs. She duped Claudius and manipulated him into executing those who displeased or spurned her. She is also recorded as a lover of parties and festivities as well as an enthusiastic player of court politics who sold her influence to Roman nobles and foreign notables. Her name is now used as a synonym for others with her supposed vices.
Messalina bore him a daughter (Octavia, born in 39) and a son (Britannicus, born in 41): she was therefore the mother of the heir-apparent and enjoyed influence for that reason.
Messalina's influence is indicated by her appearance on the obverse of coins of Claudius's reign (where one would expect the head of the emperor), or in the cameo now in Paris depicting Messalina, Octavia, and Britannicus.
Messalinas birthday was officially celebrated, statues of her were erected in public places and she was given the privilege of occupying the front seats at the theater along with the Vestals.