Sykes, known as one of the league's top perimeter defenders, spent the past three seasons with the Los Angeles Sparks after playing her first three years with the Atlanta Dream, who chose her No. 7 in the 2017 WNBA draft.
"Brittney was a main target for us in free agency," Mystics general manager Mike Thibault said. "She brings a skill set to our backcourt that perfectly complements our other perimeter players. Her speed in transition, ability to get to the basket or find open teammates, will allow us to accelerate our offensive pace and flow."
Sykes, a 5-foot-9 guard, has averaged 11.1 points, 3.9 rebounds and 2.5 assists in her WNBA career. A a Newark, New Jersey, native who starred at Syracuse, she has led the league in steals the past two seasons and has been on the All-Defensive first or second teams the past three seasons.
"She can play offense and defense at three positions," Thibault said. "And as one of the premier defensive guards in the league, she will help us continue to excel as one of the best defensive teams in the WNBA."
The Mystics, winners of the 2019 WNBA title, had the best defensive rating in the league last season (97.8), when they went 22-14 and lost in the first round of the playoffs to the Seattle Storm.
Among other deals Wednesday:
• Veteran guard Kristi Toliver is also leaving Los Angeles to go to Washington. Toliver previously played for the Mystics from 2017 to 2019 and was part of their 2019 championship team. The Virginia native and Maryland grad was the No. 3 overall pick in the 2009 draft by the Chicago Sky, and has won titles with both the Sparks and the Mystics. She has averaged 12.0 points and 3.5 assists in her 13-season career, which includes two stints in Los Angeles for nine seasons total.
• Forward Stephanie Talbot has signed for two years with the Sparks after spending the past two seasons with the Seattle Storm. The native of Australia has averaged 4.8 points and 2.6 assists in her five-season WNBA career. Guard Lexie Brown, also an unrestricted free agent, opted to stay with the Sparks. This will be her sixth WNBA season and second with Los Angeles. She averaged 7.1 points and 2.1 assists last season.
• Center Teaira McCowan, a restricted free agent, has signed a multiyear deal to remain with the Dallas Wings. The Texas native was drafted No. 3 in 2019 by the Indiana Fever, and then traded before the 2022 season to the Wings. She averaged 11.0 points and 7.0 rebounds for Dallas last season. "I am so excited to continue to play for the Wings organization and to be able to call Dallas home for years to come, as this is where I wanted to be all along," McCowan said.