Updated 10:58 a.m. ET, 1/27/2014
Washington (CNN) - U.S. Rep. Trey Radel, the Florida Republican who pleaded guilty to cocaine possession last November, will resign from Congress on Monday, he wrote in a resignation letter to House Speaker John Boehner.
Radel was caught buying cocaine from an undercover federal agent in Washington and spent nearly a month in a substance abuse program in Florida.
[twitter-follow screen_name='politicalticker'][twitter-follow screen_name='deirdrewalshcnn'][twitter-follow screen_name='psteinhausercnn']
"Unfortunately, some of my struggles had serious consequences," he said in the letter. "While I have dealt with those issues on a personal level, it is my belief that professionally I cannot fully and effectively serve as a United States Representative to the place I love and call home, Southwest Florida."
His resignation is effective as of 6:30 p.m. ET, Monday.
Upon returning to Capitol Hill this month, Radel apologized for his actions and insisted he was not yet thinking about re-election to another term.
"I cannot express how sorry I am. I ask for your forgiveness. I've let down our entire country. I have let down my colleagues on both sides of the aisle. I've let down my family," an emotional Radel said in a brief session with reporters in his office on Capitol Hill, his voice often halting.
Radel, who was known for his casual demeanor and his accessibility to reporters, appeared stoic and stuck with a serious message that he wanted to earn back his reputation, which was crushed by his bust in the undercover sting last fall.
The former television anchor avoided cameras and national media and made a brief statement inside his office, with his aides insisting his comments be off-camera.
"In front of a U.S. representative's name, they often put the word 'honorable,' and I will work hard every day to restore that honor - rebuilding trust and making amends, with our country, my constituents, my colleagues, my wife and my 2-year-old."
Although he declined to detail his treatment plans, Radel made several references suggesting he was participating in an Alcoholics Anonymous 12-step program. Although he was arrested for drug possession last fall, he said afterward that his bigger struggle was with alcohol abuse.
"I have an incredible network both at home and right here in Washington, and this is something I will continue to work on for the rest of my life. I will take it one day at a time, and in doing so, I hope to rebuild and regain trust one day at a time," he said.
Radel represents Florida's 19th Congressional District, a solidly Republican district that stretches along the Gulf Coast from Fort Myers south to Naples and Marco Island. He was already facing a primary challenge from a former state lawmaker in August's GOP primary, and other Republicans were expressing interest in the seat.
It's up to the state's GOP governor, Rick Scott, to decide when a special election will be held.
CNN's Paul Steinhauser and Chris Frates contributed to this report.