Lewis, an Army National Guard (search) captain who served in Iraq, picked the second anniversary of the fall of Baghdad to announce his plans. The Morgantown lawyer made his announcement near the base of a statue of West Virginia's senior Democratic senator at the state Capitol in Charleston.
"My candidacy is not a personal vendetta against the senior senator; rather it is simply time for a change," said Lewis, who lost the GOP nomination to challenge Democrat Sen. Jay Rockefeller (search) in 2002. Lewis came close to upsetting Democrat Attorney General Darrell McGraw (search) in November.
Byrd has been targeted by the National Republican Senatorial Committee (search) for defeat in next year's election. The 87-year-old Byrd has served 45 years in the Senate and has yet to declare his re-election bid, but his office has said he intends to seek a ninth, six-year term. Byrd spokesman Tom Gavin could not immediately be reached for comment on Saturday.
Lewis, 34, said he is not running "against" Byrd, but "with" him.
"I believe we both have the interests of West Virginians at heart. It is just that we disagree over the way to protect and serve those interests," Lewis said.