Cicero maybe? Marcus was his name also. He was a lawyer too.

Not famed for his soldierly ability, though, Cicero. Despite what he'd tell you about quashing the rebels in Cilicia.

Not sure I can think of anyone with all those features you mention.

The Loeb classical library has a full list extant texts, and perhaps a name will ring a bell. Here's a link:

http://www.hup.harvard.edu/loeb/author.html

He was a lawyer, and possibly the greatest orator Rome ever produced, and although not the greatest of soldiers, he was one also for a short stint. So Cicero does fit all of the criterion mentioned.

He died quite some time prior to the AD's though, so he doesn't meet all the criteria.

Plus being of humble birth, he had only the three names: Marcus Tullius Cicero.

The original post never stated the amount of names.

He believes it was written in AD.

Sincerely