Captain Duvall was a Starfleet officer during the mid-22nd century. (ENT: "Fusion")
In 2144, Duvall was a pilot in the NX test program and the first Human to break warp 3 in the NX-Delta prototype - after first choices A.G. Robinson and Jonathan Archer had some trouble with authority after making an unauthorized test flight to avoid the closing of the program. (ENT: "First Flight")
In 2151, Duvall was given the command of the Earth starship Shenandoah. (ENT: "Silent Enemy")