The team announced the agreement Tuesday. No terms were disclosed.
The Revolution said the 35-year-old midfielder will be at the team's training session at Gillette Stadium on Wednesday.
Ralston spent eight seasons with the Revolution before signing as a player/assistant coach with his hometown AC St. Louis of the second-division in January.
In addition to the MLS record for assists with 135, Ralston holds the league mark in appearances (378), starts (372) and minutes played (33,143).
Last year, Ralston had surgery to repair a torn anterior cruciate ligament in his right knee.