Adams was being sued in London's High Court for allegedly being directly responsible and complicit for decisions by the Provisional IRA to detonate bombs in England in 1973 and 1996. He was being sued for a symbolic 1 pound ($1.34) in damages.
Adams, 77, who gave evidence in the trial but who was not in court Friday, welcomed the decision by the claimants and said he had "nothing but sympathy" for them.
"But at times it verged upon a show trial, anonymous secret agents of the British state hiding behind the screen, others who were up to their necks in the subversion that the British state visited upon people of this part of the island of Ireland," he said in Belfast surrounded by Sinn Fein lawmakers.
Adams is one of the most influential figures of Northern Ireland's decades of conflict. He led the IRA-linked political party Sinn Féin between 1983 and 2018 and helped broker the 1998 Good Friday peace accord. He has always denied being an IRA member, though some former colleagues have said he was one of its leaders.
The trio claimed Adams was a member of the IRA's decision-making Army Council and was as responsible as the men who planted the explosives during "the Troubles," the three decades of violence involving Irish republican and British loyalist militants and U.K. soldiers. Some 3,600 people were killed, most in Northern Ireland, though the IRA also set off bombs in England.