The legal claim alleges agent Brian Dreyfuss was cut out of negotiations regarding the blockbuster franchise.
He sued Johnson in Los Angeles Superior Court on Friday, seeking 10% of the director's Star Wars earnings.
Mr Dreyfuss claims he arranged a meeting between Lucasfilm president Kathleen Kennedy and Johnson in 2012.
He also says Johnson told him he was not interested in working on any of the film company's projects.
The agent's legal claim states he was fired in March 2014, about a year before Johnson confirmed he would direct the eighth film in the Star Wars franchise.
The movie, which has just begun shooting, is due to be released in December 2017.
New cast members will include Benicio Del Toro and Laura Dern, alongside Episode VII stars such as Mark Hamill, Carrie Fisher, Adam Driver, Daisy Ridley, John Boyega, Lupita Nyong'o, Domhnall Gleeson and Andy Serkis.
Mr Dreyfuss claims he began working with Johnson around 2002 and helped him develop his first film, Brick.
He says he also encouraged Johnson to direct several episodes of the hit TV series Breaking Bad and the 2012 film Looper, starring Bruce Willis and Joseph Gordon-Levitt.
Johnson's publicist could not be reached at the time of writing.
A former agent for Rian Johnson, the director of the upcoming Star Wars: Episode VIII, is suing the film-maker two years after he was fired.