Sa vérité est en marche.

English Translation

His truth is marching on.

No idea what this is supposed to mean, the English sentence doesn’t mean anything.

I think “la vérité est en marche” is more common as an idiom. It’s famously in Émile Zola’s “J’accuse”:

Je le répète avec une certitude plus véhémente: la vérité est en marche et rien ne l’arrêtera.

Translated :

I repeat it with a more vehement certainty: the truth marches on and nothing will stop it

Nowadays “la vérité est en marche” is generally used to mean something like “the cat is out of the bag”, although personally I would probably mainly use it ironically since it sounds a bit pompous in my opinion.