By 54 BC Marcellus had married Octavia the Younger, a great-niece of Julius Caesar (and sister of future emperor Augustus), in an arranged ceremony.

However, according to the anonymous Περὶ τοῦ καισαρείου γένους Octavia bore Marcellus four sons and four daughters.

[1][2] Because of Marcellus relatively advanced age at the time of his marriage to Octavia, it has been suspected by Ronald Syme that he might have been married before to a woman who is not attested.

[3] Christian Settipani has speculated that Marcellus might have had a daughter by an earlier wife who married the Roman senator Sextus Quinctilius Varus (who served as a Quaestor in 49 BC).

However, Pompey apparently declined the proposal and Octavia's husband continued to oppose Julius Caesar, culminating in the crucial year of his consulship in 50 BC when he tried to recall Julius Caesar from his ten-year governorship in Gaul two years early, without his army, in an attempt to save the Roman Republic.