SPRINGFIELD, Ill. — Illinois state Rep. Michael Madigan, a Chicago Democrat who virtually set Illinois’ political agenda as House speaker before he was ousted last month, announced Thursday that he is resigning his seat in the Legislature.

Madigan, who was elected speaker in 1983 and served 36 of the next 38 years at the helm, was tarnished by a federal investigation of Statehouse bribery announced last summer that implicated him. He has not been charged with wrongdoing and maintains his innocence. But he lost his bid for a 19th term as speaker to Hillside Democrat Emanuel “Chris” Welch.

In a statement Thursday, Madigan, 78, said he was resigning as state representative at the end of the month. He didn’t say explicitly why he was resigning the post he has held for 50 years, but blamed a whispering campaign for the loss of trust in him.