WASHINGTON — With a disappointing election in his rear view mirror and a budget compromise he could never swallow on the horizon, Senator Jim DeMint, the conservative Republican from South Carolina who helped ignite the Tea Party movement, is leaving the Senate to become president of the Heritage Foundation, a conservative research group.

Just two years into his second term, Mr. DeMint, 61, whom many in his own party partly blame for Republicans failing to win Senate control two elections in a row, announced on Thursday that he has opted for a platform and a payday that the United States Senate could never provide him.

His resignation also comes as Tea Party followers in Congress face new pressure to pull back from their uncompromising views in the election’s aftermath. He will depart with the start of the new Congress in January.

Come January, the occasional kingmaker, conservative hero and filibuster lover — he once forced the Senate to stay in town for a Saturday vote that he then chose to skip — will find himself with a space to continue his efforts to push the Republican Party to the right from the outside rather than the inside.