Produced by T Bone Burnett, "The Union" is set for U.S. release Oct. 19 on Decca. It is to drop in the United Kingdom Oct. 25 on Mercury Records.
The album marks the first time the iconic artists have worked together since 1970, Decca said in a news release.
"The Union" was recorded live in the studio and features songs written by John and his longtime lyricist Bernie Taupin, as well as in combination with the talents of Russell and Burnett, the label said.
"In the late '60s and early '70s, the one piano player and vocalist who influenced me more than anybody else was Leon Russell," John, 63, said in a statement. "He was my idol."
The pair toured together for awhile, then fell out of touch. John listened to Russell's music while on safari in Africa last summer and was inspired to reconnect with him, Decca said.
"Elton called to ask if I would do a duet album with him," Russell, 67, said. "I'm very happy that he chose me to do this."