I know under the Late Republic Senators where recruited to fill officer roles, but I want to know if the Romans ever established something like the modern officer corps made up of career officers who transferred between line units and HQ posting as they moved up the ranks. Did this ever happen in the Roman Army or was this strictly a more modern invention?
Edit: After the period when the realms of political and military spheres were separated.
You will most likely have to clarify your time frames a little bit since the career paths would have changed over time.
By the third and fourth century you would have seen a split between military and political office which was very much in contrast to the warrior politicians of the republic. This change was an attempt by Diocletian to prevent individuals from gaining too much power through both combined military and political control.
The empire would have also started to see the promotion of more equestrians rather than senators. I can't speak too much about the specifics of an officer but hopefully my comments can shed a bit of light on the political landscape and how certain career paths from earlier times were no longer possible.