The longtime politician turned 100 on Tuesday ... after spending the last 19 months in hospice care. He is the only U.S. President to live to 100.

Carter served as the 39th president of the United States after previously serving as the 76th governor of Georgia. The former president has always been dedicated to service ... whether it was his time in the Navy or his volunteer work with Habitat for Humanity.

And Carter plans to continue to do his civic duty heading into this year's presidential election. According to Carter's grandson, Jason Carter, the longtime Democrat is hoping to stay alive long enough to "vote for Kamala Harris."

However, Carter has certainly taken a large step back from the limelight ... making a rare public appearance at wife Rosalynn Carter's funeral back in November. The former First Lady passed away at age 96 after battling dementia and other health issues.

Carter himself is struggling physically, and was notably confined to a wheelchair at his wife's service.

While Tuesday marked Carter's big birthday, a star-studded tribute concert was held last month in Atlanta in his honor.

The event, titled "Jimmy Carter 100: A Celebration in Song," featured performances from Chuck Leavell, D-Nice, Drive-By Truckers, GROUPLOVE, Eric Church, Maren Morris, The War And Treaty, and the Atlanta Symphony Orchestra Chamber Chorus.

The concert is set to be streamed on Georgia Public Broadcasting ... and Carter is even expected to tune in.

Birthday wishes are expected to pour in for Carter ... who already received a video tribute from President Joe Biden. In the footage, Biden declared he admired Carter "so darn much" and wished him a happy birthday.

The White House also put up a "100" display on the North Lawn in honor of the major milestone.