English Translation
He had a meal together with us.
共に for “together” is more often used in formal writings, and it could even sound a bit poetic. 我々 for “us” is also very formal. Therefore, the whole sentence sounds like we all are military comrades or something like that.
Even if the original author (translator) meant the comrade storyline, the word order still bugs me. I feel:
彼は我々と食事を共にした（しょくじをともにした）。
sounds more natural.
一緒に（いっしょに）is interchangeable, and widely used in conversations as well as in standard writings. I would propose an alternative translation:
彼は私たちと一緒に食事した。