Walcott had roles in many television series, including that of Stone Kenyon in two episodes of the NBC sitcom, The People's Choice with Jackie Cooper. He was frequently cast in westerns like Bonanza (seven times), Maverick, Frontier Doctor, Wagon Train, The High Chaparral, 26 Men, Sugarfoot (with Will Hutchins and cast opposite another guest star, Joi Lansing, in the 1958 episode "Bullet Proof"), Laramie, The Rifleman, The Tall Man, The Dakotas, and in several episodes of CBS's Rawhide, through which he began a long collaboration with Clint Eastwood. Walcott had featured roles in Eastwood's films Joe Kidd (1972), Thunderbolt and Lightfoot (1974), The Eiger Sanction (1975), and Every Which Way But Loose (1978).