While performing in West Virginia, Hart was discovered by Lawrence Welk who was there for a luncheon on behalf of the Cancer Crusade. Impressed with his talent, the maestro signed him as a member of the Champagne Music Makers, where he made is first network television appearance in July 1969.
Hart replaced Lynn Anderson as the show's resident country singer and remained on the show in that capacity until 1975, when Ava Barber replaced him. During Hart's time on the show, he was nominated for a Grammy in 1969 with his first hit record "Spring", but lost to Johnny Cash, and has released a solo album, Clay Hart: Most Requested Country Favorites from the Ranwood Records label.
He married Welk vocalist Sally Flynn on December 6, 1974, and the two later became a husband-and-wife country singing act that has opened for stars such as Mel Tillis, Red Skelton, and Juliet Prowse. Recently, he and Flynn have appeared in wraparound segments for reruns of the Welk Show on PBS and have toured the U.S. with their fellow Welk stars in the Forever Blowing Bubbles concert series.
Hart has two children, Elizabeth and Hank, from a previous marriage. Since the show, he has appeared on The Nashville Network, and has operated a tote bag business with Flynn. They currently make their home in Miami, Florida.