Fyodor Simashov made his international début at the 1968 Olympics, where he finished 26th in the 15 km. At the 1970 World Championships Simashov won his first title in the relay, won bronze in the 15 km and was fourth at 50 km. At the 1972 Olympics Simashov was sixth in the 30 km, before winning a silver in the 15 km behind Swedish Sven-Åke Lundbäck. He then placed eighth in his final individual event, the 50 km and won a gold as a member of the Soviet relay team. Simashov made his last international appearance at the 1974 World Championships, where he won silver as a member of the Soviet relay team. Domestically Simashov won twelve Soviet titles – one at 15 km (1968), three at 30 km (1969, 1971, 1973), one in the 50 km (1974) and seven in the relay (1968-70, 1972, 1973, 1975, 1976). After his sporting career Simashov worked as a sports official in Zainsk.