Birch Bayh, the liberal former senator from Indiana whose work in Congress had an enduring impact on American life — in protecting women from sex discrimination in education, guaranteeing 18-year-olds the right to vote and providing for the removal of a sitting president — died on Thursday at his home in Easton, Md. He was 91.

The cause was pneumonia, the family said in a statement announcing his death.

Mr. Bayh, a Democrat who served in the Senate from 1963 to 1981, drove some of the most historic legislation of his era. He was the principal architect of two constitutional amendments: the 25th, which dealt with presidential disability and vice-presidential vacancies, and the 26th, which gave 18-year-olds the vote in both state and federal elections.

He was a chief Senate sponsor of the failed Equal Rights Amendment, which would enshrine in the Constitution protections against discrimination on the basis of sex. He pushed through another amendment that would have abolished the Electoral College and had presidents elected by direct popular vote, lining up strong support in the Senate but failing in the end to muster enough votes to send it to the states for ratification.

And he championed Title IX, drafting the language for that landmark federal legislation, which barred sex discrimination at schools and colleges and greatly expanded sports programs for women.