Senator Robert C. Byrd, Democrat of West Virginia, who is already the longest-serving senator in United States history, is set to cross yet another milestone of longevity in the legislative branch. On Wednesday, he’ll surpass Carl Hayden as the longest-serving member of Congress in history, combining terms in both the House and Senate.

Mr. Hayden, an Arizona Democrat, served in the House from 1912 to 1927 and in the Senate from 1927 to 1969 for a total of 56 years 319 days.

Mr. Byrd, whose 92nd birthday is Friday, served in the House from 1953 to 1959 and has been in the Senate ever since. He served as the Democratic leader from 1977 to 1989, about half of that time as the majority leader.

Expect numerous tributes in the Senate and in West Virginia, Gov. Joe Manchin and state lawmakers have scheduled a celebration on Wednesday at the State Capitol.