He joined the Leafs in 1957 and was a 20-goal scorer in his first season, winning the Calder Memorial Trophy as rookie of the year in what was otherwise a rough season with the last-place Leafs. During the off-season, he took courses at Assumption University in Windsor, Ontario. At the same time, Punch Imlach was hired to run the Leafs and soon became head coach and general manager.
In the 1960–61 season, Imlach put Mahovlich on a line with Red Kelly and Bob Nevin. The three immediately clicked and were the team's top three scorers that year, led by Mahovlich's 48 goals—a Leaf record that would stand for 21 years. The following season, the Leafs won the Stanley Cup, and repeated as champions in 1963 and 1964. Mahovlich led the team in goals scored in all three seasons.
Initially, Mahovlich and Imlach got along well, but their relationship deteriorated after winning the 1962 Stanley Cup, particularly when Mahovlich's contract was up for renewal at the end of the 1962 season. He felt the Leafs gave him a low-ball offer and walked out on the team during training camp in September. Red Burnett at the Toronto Star described the situation as a "cold war" between Imlach and Mahovlich.
At that time, the National Hockey League All-Star Game was played at the beginning of the season, and during a reception in Toronto attended by team executives in the days before the 1962 game, Chicago Black Hawks owner James D. Norris offered the Leafs $1 million for Mahovlich. He believed he had an agreement with Leafs co-owner Harold Ballard and paid $1,000 as a deposit with the balance to be delivered by cheque the next morning. The next day, the Leafs gave Mahovlich the money he had been asking for and told the Black Hawks that their apparent agreement the night before had been a misunderstanding. The Leafs returned the $1,000 deposit. The Black Hawks accused the Leafs of reneging on a deal. Conn Smythe, at this point a minority shareholder in the Leafs, was adamant that the deal should be rejected. Mahovlich eventually spoke out publicly and reaffirmed his commitment to the Leafs.
Mahovlich also had a rocky relationship with fans at Maple Leaf Gardens and was often booed at home games. Imlach—who mispronounced Mahovlich's name for years—became a constant critic and, under pressure from fans and management, Mahovlich was admitted to Toronto General Hospital in November 1964, suffering from what was publicly described as "constant fatigue" but diagnosed as acute depression. Mahovlich was flooded with well-wishes from fans during his time off. He returned to the lineup a month later and was still able to lead the Leafs in scoring in the 1964–65 season, despite missing 11 games. Mahovlich led the Leafs in scoring again in the 1965–66 season.
The Leafs won the Stanley Cup in the 1966–67 season, with Mahovlich having his lowest-scoring year in seven seasons. Early into the next season, Mahovlich was again admitted to hospital, although this time it was acknowledged publicly as depression and tension. "Mahovlich is a sensitive, easily-bruised individual," wrote Milt Dunnell in a page-one story in the Toronto Star.
Mahovlich was part of a six-player blockbuster transaction in which he was traded along with Pete Stemkowski and Garry Unger from the Maple Leafs to the Detroit Red Wings for Norm Ullman, Paul Henderson and Floyd Smith on March 4, 1968. The Maple Leafs and Red Wings were in fifth and sixth place respectively at the bottom of the East Division standings. He had 19 goals and 17 assists in 50 games that season and was the leading goalscorer in Maple Leafs franchise history with 296 at the time of the deal.[3] He joined a Red Wings team that also featured his younger brother Pete. He said in a press conference announcing the trade, "Business is business and if I can't please them here, maybe I'll be able to please them there."[4]
Mahovlich had a strong finish to the season with the Red Wings, and the following year put up his best point totals in eight seasons, playing on a line with Gordie Howe and Alex Delvecchio, and setting his record for goals in a season with 49. Initially, one of his teammates on the Red Wings was his younger brother, Peter Mahovlich, who split his time between the Wings and their minor league affiliate.
In 1970–71, Red Wings general manager Sid Abel wanted to get rid of coach Ned Harkness and was overruled by team owner Bruce Norris. Once Harkness took over as general manager, he got rid of players he deemed a threat to him. On January 13, 1971, Mahovlich was traded to the Montreal Canadiens for Mickey Redmond, Guy Charron, and Bill Collins. He was reunited with his brother, who had become a star player himself with the Canadiens. Mahovlich spent three-and-a-half seasons in Montreal, playing on the Stanley Cup-winning teams of 1971 and 1973. During the 1971–72 season, Mahovlich scored a career-high 96 points, which he nearly matched the following season with 93 points.
He attempted an NHL comeback with the Detroit Red Wings in 1979, but it was unsuccessful, and he formally retired on October 7, 1979.
In an NHL documentary about the Stanley Cup, Mahovlich claimed credit for being the first player to hoist the Stanley Cup above his head. After the Leafs' victory in the 1962 Cup Finals, in the team locker room, Mahovlich said he held the Cup, felt how light it was, and hoisted it above his head, which was then photographed.[6]
In 1997, Mahovlich was ranked number 26 on The Hockey News's list of the 100 Greatest Hockey Players, the highest-ranking player who had spent at least a majority of his career with the Maple Leafs.
In 1998, Mahovlich was appointed to the Senate of Canada by Prime Minister Jean Chrétien. He retired from the senate on January 10, 2013,[9] at the mandatory retirement age of 75.
