Dennis Kearns was an excellent puck-moving defenceman with a good shot from the point who spent his entire ten-year NHL career with the Vancouver Canucks. He was useful on the power-play and with the team's transition game but he needed to be paired with someone who would stay back when Kearns embarked on one of his rushes or was pinching in at the blueline.

Kearns played junior with the hometown Kingston Canadians of the OHA in 1965-66 then spent a year with the city's senior Aces. Originally property of the Chicago Black Hawks, Kearns was a stalwart in WHL with the Portland Buckaroos from 1967 to 1970. He scored 117 points in three years and was voted on to the league's second all-star team 1969 and the first all-star squad in 1970. Kearns then spent the 1970-71 season with the CHL's Dallas Black Hawks where he scored 52 points and was named to the league's first all-star team.

Around this time Chicago was deep on defence and decided to expose Kearns in the Intra-League Draft. He was claimed by Vancouver on June 8, 1971 and embarked on a successful 677-game career. The young blueliner scored 29 points for the Canucks as a rookie in 1971-72 and became a fixture on the team's defense. During this period he was often paired with Dale Tallon or John Schella. Offensively Kearns put up his most impressive numbers between 1975 and 1978 when he recorded 158 points in those three years. He registered 60 points in 1976-77, a team record until Doug Lidster broke it with a 63-point effort in 1986-87.

Kearns mobility and offensive savvy were sought by Team Canada at the 1977 and 1978 World Championships. By the 1979-80 season, Kearns was slowing down and the team was giving Lars Lindgren and Kevin McCarthy more ice time and power play work. The veteran rearguard retired after playing 46 games in 1980-81.

Kearns finished his career with 31 goals and 290 assists for 321 points in 677 games, adding 386 penalty minutes. His 55 assists in 1977 remained the franchise record for defencemen until surpassed by Quinn Hughes in 2022 with 60 assists. His 321 career points was the all-time mark for Canucks defencemen for over three decades until surpassed by Mattias Öhlund at the end of the 2009 season. His 290 career assists stood as the franchise record for defenceman until being overtaken by Alexander Edler in 2020.

In retirement, he and his family live in Vancouver, where he owns an insurance business. His son, Bracken Kearns, also played hockey professionally with the Florida Panthers, San Jose Sharks, and New York Islanders before retiring in 2019.