Rep. John Lewis, D-Ga., was released from an Atlanta hospital Sunday, one day after he was hospitalized for "routine observation."

"All tests have been completed and doctors have given him a clean bill of health," Lewis spokeswoman Brenda Jones said in a statement. "[Lewis] thanks everyone who shared their thoughts, prayers and concerns during his stay."

Earlier Sunday, Jones told The Associated Press Lewis was "resting very comfortably" and would stay in the hospital until doctors' observations were complete.

Lewis had been expected at an Atlanta event Saturday evening, but did not attend.

The 78-year-old Lewis played a key role in the civil rights movement and marched with the Rev. Martin Luther King Jr. in 1965 in Selma, Ala. He is the youngest and last survivor of the so-called "Big Six" civil rights activists, led by King Jr.

Lewis was best known for leading some 600 protesters in the 1965 Bloody Sunday march across the Edmund Pettus Bridge in Selma. At the head of the march, Lewis was knocked to the ground and beaten by Alabama state troopers. His skull was fractured. Televised images forced the country's attention on racial oppression in the South.

Lewis was first elected to Congress in 1986 and is running unopposed for re-election later this year.

The Associated Press contributed to this report.