Marcus Foslius Flaccinator was a Roman statesman who served as a member of the tribuni militum consulari potestate in 433 BC alongside Marcus Fabius Vibulanus and Lucius Sergius Fidenas. He later served as Pontifex Maximus.

The gens Foslia was a patrician family at Rome. The first of the gens to appear in history was Marcus Foslius Flaccinator, consular tribune in 433 BC.