He is regarded as one of the most iconic Celtics figures in the franchise's history, known during his lifetime for his charisma and loyalty to the team and its traditions.

Heinsohn was the only person to have the distinction of being involved in an official team capacity in each of the Celtics' first 17 championships, as well as each of their first 21 NBA Finals appearances.

He finished his rookie season by winning his first championship ring, scoring 37 points and grabbing 23 rebounds in the double-overtime 7th game of the NBA Finals.

[3] On the day his teammate and fellow Holy Cross Crusader Bob Cousy retired, Heinsohn scored his 10,000th career point.

Initially, the team missed Russell's impact, and the Celtics struggled in both 1969–70 and 1970–71, failing to reach the playoffs in both seasons.

Heinsohn then led the team to a league-best 68–14 record during the 1972–73 season and was named Coach of the Year, although Boston was upset in the playoffs by the eventual champion New York Knicks.

Heinsohn would leave the team shortly thereafter, replaced by his former teammate and coaching assistant Tom "Satch" Sanders.

On February 14, 2015, it was announced that Heinsohn would be inducted into the Basketball Hall of Fame for a second time as a coaching inductee.

In 1981, Heinsohn joined Mike Gorman as color commentator on PRISM New England, which held the Celtics' television broadcasts.

[permanent dead link‍] During broadcasts he was known for his sense of humor and indignantly questioning game officials when he felt calls against the Celtics were made in error.

For a time in the 1980s, Heinsohn was in the same capacity during CBS's playoff coverage of the NBA (with Dick Stockton), calling four Finals from 1984 to 1987, three of which involved the Boston Celtics against the Los Angeles Lakers.

[10] Away from the court, Heinsohn enjoyed painting and playing golf; he once headed a life insurance company.