Tannen's first credited role was as Luther Botts in 1934 in the film short, "My Grandfather's Clock." Most of his early film roles were uncredited. In 1954, he played Emmett Dalton in the film, Jesse James vs. the Daltons. Brett King played the role of Joe Branch, reputed son of Jesse James in this historically inaccurate picture. That same year, Tannen played O'Connor in the film Sitting Bull, with J. Carrol Naish in the title role. and Iron Eyes Cody as Crazy Horse, and also starring Dale Robertson.
Tannen was also cast as Gyp Clements in the 1955 episode "The Buntline Special" of The Life and Legend of Wyatt Earp. Beginning on September 11, 1956, in the second season of the series, with the setting moved from Wichita to Dodge City, Kansas, Tannen filled the Hal Norton role. His earliest episodes were "Fight or Run", "The Double Life of Dora Hand" and "Clay Allison", the latter two based on historical figures, the saloon singer and actor Dora Hand and the gunfighter Clay Allison. Some of his appearances were uncredited. His last credited role was "Doc Holliday Rewrites History" (May 6, 1958), with Myron Healey as the frontier gunfighter and dentist Doc Holliday. His last uncredited roles aired thereafter in May and June 1958, "Dig a Grave for Ben Thompson", based on the historical figure Ben Thompson played by Denver Pyle, "Frame-up", and "My Husband".
On May 1, 1960, Tannen portrayed Jim Ashbury in the episode "Backwater Swamp" of the ABC/Warner Brothers western series, Sugarfoot, starring Will Hutchins in the title role. James Coburn, Robert Colbert , and Kevin Hagen appeared in this episode as Rome Morgan, Ben Crain, and Sam Fields, respectively.
While most of Tannen's work was in westerns he was cast as a colonel in an episode of the ABC situation comedy My Three Sons, starring Fred MacMurray, a newscaster in a 1962 episode of the short-lived NBC drama series, Saints and Sinners and in three episodes in 1960, 1964, and 1966 of CBS's Perry Mason, starring Raymond Burr in the title role. He also appeared with Mike Connors in the 1959 episode "The Cracking Point" of the CBS series Tightrope, in the ABC series, Target: The Corruptors!, and in two episodes of The Detectives, starring Robert Taylor.
He was cast as Ike Clanton, not on The Life and Legend of Wyatt Earp, but in the 1964 episode "After the OK Corral" of the syndicated western anthology series, Death Valley Days. Jim Davis portrayed Wyatt Earp in this particular episode. Tannen appeared twice, one role uncredited in Davis' earlier syndicated western series, Stories of the Century, including the role of Dutch Charlie in "Milt Sharp", the story of the stagecoach robber Milt Sharp.
His last role was in 1969 as a minister in the episode "Little Darling of the Sierras" of the CBS western series, Lancer (TV series), starring Andrew Duggan, James Stacy, Wayne Maunder, and Paul Brinegar, who had appeared with him a decade earlier on episodes of The Life and Legend of Wyatt Earp in the role of the historical figure, James H. "Dog" Kelley.
