Billy Jack (Tom Laughlin) is appointed a United States Senator to fill out the remaining term of another senator. It is hoped that he will quietly vote the party line, but his term in the Senate runs into trouble when he proposes a bill to fund a national youth camp which happens to be on the property where a nuclear power plant is also being proposed. His fellow senator, Joseph Paine (E. G. Marshall), claims to oppose nuclear power but is secretly taking graft to influence his votes in favor, and moves to try to keep Billy Jack out of the way when the bill is being debated.
Seeking to keep Billy out of the Senate on a day when a controversial energy bill is being voted on, Senator Paine suggests he should meet with a grassroots group that day instead. The group is working to pass a national initiative and Billy Jack becomes convinced of their cause.
Billy is invited to meet with a group of lobbyists attempting to offer him bribes and other perks if he will vote their way. Up against a man named Bailey (Sam Wanamaker) who wields a powerful influence in his home state, Billy Jack has his political career and reputation at stake if he does not cooperate. Billy responds with anger at their threat.
The next day in the Senate, he tries to speak on the floor in opposition to the nuclear power plant. Paine responds by proposing to expel Billy from the Senate as unfit for office. Billy's assistant quits after the murder of a lobbyist, fearing for her own safety, but returns after Billy Jack is about to be expelled from the Senate, to help him learn Senate procedure in order to filibuster. Billy collapses on the Senate floor in the effort, whereupon Paine confesses to his colleagues that every word Billy spoke was the truth.Tom Laughlin as Billy Jack
E.G. Marshall as Paine
Lucie Arnaz as Saunders
Delores Taylor as Jean
Suzanne Somers as Sue
Sam Wanamaker as Bailey
Peter Donat as Butler
Pat O'Brien as the Vice President
As with the two previous films in the series, Laughlin's wife Delores Taylor and daughter Teresa Laughlin reprise their roles. Julie Webb and several other supporting actors from Billy Jack and The Trial of Billy Jack return as well. Author and political journalist Joe Klein appears briefly as a reporter in the opening scene. (Klein became friends with Laughlin after interviewing him for Rolling Stone in 1975.)
A new version of the song "One Tin Soldier" (the original theme for Billy Jack) sung by Teresa Laughlin is played over the closing credits.
Billy Jack Goes to Washington was a failure, partly due to distribution problems, and it proved to be Laughlin's last film as a director. Laughlin blamed individuals within the United States government for the failure of the film, telling CNN's Showbiz Tonight in 2005:
At a private screening, Senator Vance Hartke got up, because it was about how the Senate was bought out by the nuclear industry. He got up and charged me. Walter Cronkite's daughter was there, [and] Lucille Ball. And he said, "You'll never get this released. This house you have, everything will be destroyed."
Scenes featuring Suzanne Somers and William Wellman Jr. were cut from the DVD release, which is missing 40 minutes. Wellman's cut scenes had him reprising the national guardsman he played in The Trial of Billy Jack, who was now on the board of the Freedom School's directors.
The unfinished sequel to this movie is The Return of Billy Jack (1985/86).