Michael G. Hubbard, the speaker of the Alabama House of Representatives, whose sharp-elbowed approach to politics propelled the Republican Party to dominance in his state, was convicted Friday on 12 felony ethics charges, leaving him stripped of power and facing the possibility of decades in prison.

The verdict, at the end of Mr. Hubbard’s trial in the Lee County Circuit Court, deepened the political crisis in Alabama, where some of the most influential state officials are facing inquiries and threats of ouster. In recent weeks, the troubles of Mr. Hubbard, who had wielded a level of influence that easily rivaled Gov. Robert Bentley’s power, played out in public as prosecutors portrayed him as financially desperate, privately frustrated and criminally culpable for misconduct under the very ethics law he had helped to strengthen.

Although jurors acquitted Mr. Hubbard on 11 counts, his conviction on the remaining dozen charges prompted his removal as the leader of the House. Mr. Hubbard, who was convicted of improperly soliciting benefits from lobbyists and voting in favor of a measure that helped a company for which he consulted, faces up to 20 years in prison on each count.

“We hope that this verdict tonight will restore some of the confidence of the people in the state of Alabama,” said W. Van Davis, who oversaw the public corruption inquiry that led to Mr. Hubbard’s indictment in October 2014.