His son Tom and nephew Mark also became congressmen, then both were elected to the Senate in 2008.
Under Stewart Udall's leadership from 1961 through 1968, the Interior Department aggressively promoted an expansion of public lands and helped win enactment of major environmental laws, including ones to protect endangered species.
Udall, born in St. Johns, Ariz., on Jan. 31, 1920, was raised on a farm in the desert country near the Arizona-New Mexico line, an area settled in 1879 by Mormons led by his missionary grandfather. The Udalls became one of the most prominent families in the state. His father was a justice on the Arizona Supreme Court.
After World War II broke out, Udall enlisted and served as a gunner on a B-24 bomber in Italy. He returned to Arizona and finished school, receiving a law degree in 1948 from the University of Arizona. He and brother Morris opened a law practice in Tucson.
In 1954, an incumbent Democratic congressman retired and Udall won the seat in the U.S. House of Representatives representing a district that included all but the Phoenix area. He backed liberal causes in Congress, including civil rights legislation, federal aid to integrated public schools. And as a Westerner, he supported federal public works project such as dams for hydroelectric generation.
Udall worked with then-Sen. Kennedy in 1959 on labor reform legislation and helped Kennedy secure the support of Arizona's delegates to the 1960 Democratic National Convention -- votes considered safe for Johnson. Udall won re-election in 1960 but gave up the seat to accept the interior secretary appointment. Udall's brother, Morris, succeeded him in Congress by winning a special election.
Udall married Ermalee Webb of Mesa, Ariz., on Aug. 1, 1947. She died in 2001.
He is survived by six children -- Tom Udall, Scott Udall, Lynn Udall, Lori Udall, Denis Udall and Jay Udall -- and eight grandchildren.