While serving as president in 2010-2015, his homespun oratory, simple ways and social reforms such as the legalization of marijuana and gay marriage made him wildly popular abroad. But critics said his administration failed to deal with problems in education, security and environmental protection — all pillars of his presidential agenda.
Mujica still lives on a flower farm with his wife and drives an old VW Beetle. He said that after resigning as a lawmaker he plans to travel to Europe and attend the Venice Film Festival for the premiere of a movie that chronicles his life, directed by Emir Kusturica.
But Mujica added in his letter that he will not retire from politics.
"While my body is functioning, I can't renounce solidarity and the fight for ideas," he said.
Although Mujica has said he will not be a candidate in next year's election, there is speculation he resigned from the Senate so he can run for the presidency again. He also had denied he would run before he won the presidency in 2010.