In the mid-2270s, he was the commanding officer of Epsilon IX monitoring station. While communicating with the Federation starship USS Enterprise, Branch, along with the crew and station of Epsilon IX, was "absorbed" by the V'ger probe as it passed near the station. Branch's conclusion that Epsilon IX's scans were being interpreted by V'ger as a hostile action impacted the later decisions made by James T. Kirk when the Enterprise first encountered the cloud. (Star Trek: The Motion Picture)
According to the Star Trek Encyclopedia (3rd ed., p. 54),
Commander Branch was never referred to by name in the film, but his name was in the credits. Just before Star Trek I began production, David Gautreaux had been cast in the role of Commander Xon, science officer aboard the Enterprise for the proposed television series Star Trek II. When the first episode of this series became Star Trek: The Motion Picture, the character Xon was eliminated and Gautreaux was recast as Branch.