He later played for Everton, Hearts, Falkirk and American Major League Soccer (MLS) side Kansas City Wizards.
After initially claiming he would never return to Scotland, Johnston reconsidered and appeared at a press conference to announce that he would sign for Celtic at the end of his contract with Nantes.
In July 1989, Johnston opted not to return to Celtic (who had recently sold his replacement Frank McAvennie back to West Ham United) and instead joined Graeme Souness's Rangers.
[11][12] Rangers' kitman Jimmy Bell protested by making Johnston arrange his own kit and withholding from him the chocolate bars dispensed to other players until he scored against Celtic.
Johnston scored three goals in 13 games as Everton finished 13th in the first season of the new Premier League, losing his place in the first team to new signing Paul Rideout.
Despite the departure of Peter Beardsley to Newcastle United in the close season, Johnston remained out of the team during the 1993–94 campaign as manager Howard Kendall reverted to the traditional 4–4–2 formation and partnered Tony Cottee with Paul Rideout in attack.
In 1996 Johnston moved to the United States and Major League Soccer, signing with the Kansas City Wiz (later renamed the Wizards).
[16] Mo Johnston made his debut with the Scotland national team in 1984 and played regularly under manager Andy Roxburgh following his appointment in July 1986.
He had been expected to make the squad for Mexico 86 but was dropped by Alex Ferguson (caretaker manager until the end of the World Cup after the death of Jock Stein in September 1985) after a late night incident during Scotland's preparations for their play-off against Australia in November 1985, in which Johnston had disturbed a member of the coaching staff in his hotel room.
[20] On 22 August 2006, Maple Leaf Sports & Entertainment (MLSE); owners of MLS club Toronto FC, announced Johnston as Head Coach beginning their inaugural 2007 season.
[21] Before the start of the 2008 season, it was announced that Johnston was moving upstairs to fill the role of Director of Football, though he retained the title of manager, while John Carver took over coaching duties at the time.