Craig resigned his Senate seat effective September 30.
BOISE, Idaho (CNN) - With the man who will appoint his successor standing behind him, Republican Sen. Larry Craig of Idaho said Saturday he will leave Congress where he has served for nearly three decades.
"It is with sadness and deep regret that I announce that it is my intent to resign from the Senate effective September 30th. In doing so ... I hope to allow a smooth and orderly transition of my loyal staff and for the person appointed to take my place," Craig said in a brief statement.
A cheer went up in the crowd after he said he would resign, but there also were political supporters and family members nearby.
He acknowledged several political leaders at the news conference, including Idaho Gov. C.L. "Butch" Otter, a Republican, who will appoint an interim replacement for Craig who will serve until the 2008 election.
"To have the governor standing behind me as he always has, his tremendous strength for me .... is tremendously humbling," Craig said. "For any public official at this moment in time to be standing with Larry Craig is, in itself, a humbling experience."
Also standing with Craig were his wife, Suzanne, and two of their three children, and other politicians.
Craig was arrested in a restroom in June at the Minneapolis-St. Paul International Airport on suspicion of making sexual advances to an undercover police officer in the next stall. He initially denied the accusation, according to an audiotape released by police, but on Aug. 8 he pleaded guilty to a misdemeanor charge of disorderly conduct.
Senate Minority Leader Mitch McConnell, R-Kentucky, said after the announcement, "Senator Larry Craig made a difficult decision, but the right one. It is my hope he will be remembered not for this, but for his three decades of dedicated public service."
One GOP source with knowledge of the situation told CNN's Dana Bash late this week that the Republican National Committee decided against calling for Craig's resignation after top party leaders received indications that Craig himself was close to making a choice.
A number of Idaho Republicans are said to be interested in running for Craig's seat, including Lt. Gov. James Risch, considered a front-runner; U.S. Rep. Mike Simpson, and former governor and interior secretary Dirk Kempthorne.
At least three key Republicans in Congress had called for Craig's resignation while others have condemned his alleged actions while stopping short of a call for him to step down.
The 62-year-old Craig agreed this week to step down from leadership posts on Senate committees while the Senate Ethics Committee investigates the incident.
A Senate Republican leadership aide said one of the things the Ethics Committee was poised to examine was the arresting officer's statement that Craig produced a business card identifying himself as a U.S. senator after his arrest and said, "What do you think about that?"
Craig was elected to the Senate in 1990, and had been weighing whether to run for his fourth term next year. He previously served in the U.S. House.