[5] Johnston was elected to the eight-seat body, winning over 7,000 votes, finishing sixth in the at-large race.
During his first term as councillor, Johnston cited the economic downturn that the province had in 2015 was one of the council's greatest challenges.
[9] Following the decision of mayor Tara Veer to run for re-election, in August 2021 Johnston announced he was going run for city's top job in the 2021 municipal elections, stating that "its critical... that we have a mayor who has proven leadership in the community, in professional life, and the administrative life at city hall... who can lead, collaborate and serve with a dynamic council team toward a greater Red Deer".
He stated his platform would highlight economic recovery, community safety, crime prevention, fiscal management, stronger neighbourhoods, regional partnership and health care equity advocacy.
[10] As mayor, he has continued to call on the provincial government for the expansion of the Red Deer Regional Hospital in the wake of the death of a patient who was waiting in the emergency room there.