A defenceman, Park played in the National Hockey League (NHL) for the New York Rangers, Boston Bruins and Detroit Red Wings.

He even drew occasional comparisons with the Boston Bruins superstar Bobby Orr, universally acclaimed to be the greatest at his position in hockey history.

In 1972, after the team's top scorer, Jean Ratelle, was lost due to a broken ankle, he led the Rangers past the defending Stanley Cup-champion Montreal Canadiens in the first round and the West Division champion Chicago Black Hawks in the semifinals of the playoffs.

When the upstart World Hockey Association tried to lure Park away, the Rangers re-signed him to a $200,000-a-year contract that made him, briefly, the highest-paid player in the NHL.

Park, Jean Ratelle, and Joe Zanussi were traded to the Boston Bruins in a November 7 blockbuster deal that also sent Phil Esposito and Carol Vadnais to the Rangers, one that shocked everyone.

[5][6] The New York press and public had felt that Park, 27 at the time, was overweight, overpaid, and over the hill, as he was facing unfavorable comparisons to Denis Potvin.

Contrary to expectations that the Rangers had gotten the better end of the trade, the struggling Bruins were instantly rejuvenated and soon again became one of the NHL's best teams, despite the departures of Phil Esposito and Bobby Orr.

[4] Taking over the mantle of leadership from Orr, whose career was threatened by injury and who would soon leave the team, Park continued his success under coach Don Cherry.

Park earned two first All-Star team selections, while coming in second in the Norris Trophy race twice in a Bruins' uniform, with 1977–78 being considered one of his finest seasons.