Ottawa claimed a 4-3 overtime victory against Washington, and the Swedish blueliner's helper put him at 300 career NHL points in only 393 games. The 24-year-old is the fastest defenceman to earn that many points in 17 years.
Former Dallas Star Sergei Zubov was the last defenceman to reach the mark so quickly. The Russian registered his 300th point in his 354th game on Jan. 11, 1998.
Karlsson is also the second fastest Swedish defenceman to accomplish the feat, just behind Borje Salming's 388 game achievement.
Ottawa's captain won't have much time to bask in his milestone, as the Senators are deep in the Eastern conference playoff race with only four games remaining.
Karlsson won the James Norris Memorial Trophy as the league's best defenceman in 2012.