He's a writer, and was a writer and producer of The Next Generation, Voyager, and Enterprise. He's a co-creator of the latter.
Braga has a mixed record. He's notoriously despised by some fans for his apparent dislike of the original Star Trek, and some of his more ridiculous episodes (he wrote the infamous VOY: "Threshold" and equally ridiculous TNG: Genesis). But, Braga also wrote or co-wrote fan-favs, such as First Contact, Parallels, All Good Things, Flashback, The Year of Hell, and more. All in all, he's got some degree of writing credit (be it story, script, or whatever) for around 100 Star Trek eps, and 2 films.