"This is the guy we wanted," general manager Garth Lagerwey said.
The 28-year-old is expected to join the team in the next day or two, and be available for RSL's next league game, against Toronto at home on Monday.
Lagerwey said Russell will become the fastest player on the team, and allow RSL to pursue an attacking player before the league transfer window closes next month.
"We had to strengthen our depth in the midfield to allow us the freedom to do what we wanted" with another open roster spot, Lagerwey said. RSL had recently lost Carey Talley and Matias Cordoba.
Russell played collegiately at Duke - the same school that RSL coach Jason Kreis played for.