Wallroth's career within the Swedish intelligence started in 1971. He attended the Swedish Defence University in 1975 and was promoted to colonel in 1977 and senior colonel in 1978. Wallroth was head of the combined military intelligence and security service, as the Chief of Defence Staff's Operation Section 5 ("Chef Försvarsstabens operationssektion 5", CFst/Op5) from 1978 to 1982. He was appointed acting head of the Joint Operations Command ("Operationsledningen", OPL) in 1982 and was promoted to major general in 1984 and was head of the International Division at the Ministry of Defence from 1984 to 1989. The Cold War and the Swedish submarine incidents occupies a large part of everyday life, as well as Sweden's increased international commitments, including the United Nations peacekeeping forces. Wallroth was director-general and head of the National Defence Radio Establishment from 1989 to 1994, the dramatic years when the Warsaw Pact dissolved, the Soviet Union collapsed and the Soviet withdrew from the Baltics.