He was born (year unknown) in the Roman colony of Poetovio (modern Ptuj, in Slovenia), where his father, also called Marcus Valerius Maximianus, was a local censor and priest.

He was decorated for services in the Parthian war of Lucius Verus and was appointed by Marcus Aurelius to ensure the armies in Pannonia were supplied by boats on the Danube.

[1] The inscription set up in Laugaricio 179 AD (CIL III, 13439) also provides information: He was placed in charge of detachments of the praetorian fleets of Misenum and Ravenna and also of African and Moorish cavalry used for scouting duties in Pannonia.

Maximianus was then appointed procurator of Moesia Inferior; at the same time he was given a command to drive out brigands from the borders of Macedonia and Thrace.

It appears Maximianus enjoyed Marcus Aurelius's confidence, for he was then successively procurator of Moesia Superior and Dacia Porolissensis, after which he was adlected into the Senate with praetorian rank.