As an editor, he had seventeen feature film credits from 1943 to 1952, including The Big Sleep (1946) and Red River (1948).
From 1953 to 1975 he was a prolific director of episodes in many television series, including Gunsmoke and Wagon Train.
Dick Vosburgh wrote in his obituary that "After editing Hawks's next film The Big Sky (1952), Nyby turned to television, directing Ann Sothern's sitcom Private Secretary, which ran for four years.
He also directed episodes of The Twilight Zone, I Spy, Lassie, Gomer Pyle, U.S.M.C., Adam-12, Perry Mason, The Rockford Files, The Six Million Dollar Man, Ironside, and Kojak.
He did especially impressive work on such western series as Gunsmoke, Bonanza, Wagon Train, Whispering Smith, and Rawhide.