According to the club's press service, the agreement with the 25-year-old Russian is meant for one season.
Tkachev has not played in the NHL before, but played in the Quebec Major Junior Hockey League (QMJHL).
In the last season of the Kontinental Hockey League (KHL), Tkachev as part of the St. Petersburg SKA scored 38 (11 + 27) points in 45 regular season matches, and 8 (1 + 7) points in 11 playoff matches.
Earlier, Alexander Ovechkin said that he wants to end his career in Washington.