With the expansion in 1967 Smith made the Bruins for good and, partnered with superstar Bobby Orr on defence, led the NHL in plus/minus the first season the statistic was officially tabulated.

His best season was in 1971, during which he had his career high of 45 points, played in the NHL All-Star Game and finished with a plus/minus of +94, the fourth-highest total in history.

[1] He was named interim captain of the Bruins after longtime captain John Bucyk was injured, but left the team in March after a dispute, playing for the Canadian national team in the 1977 World Championships after that.

[2] He signed as a free agent with the New York Rangers in December 1977 at the importuning of old teammate Phil Esposito,[3] but his skills had significantly diminished, retired at season's end.

Smith finished his NHL career with 55 goals, 307 assists and 959 penalty minutes in 890 games.