When asked for a plea by U.S. District Judge Reggie Walton, the retired Major League Baseball pitcher said in a clear voice: "Not guilty, your honor." Clemens, wearing a suit and tie, was appearing in federal court only a few blocks away from where he swore under oath to a House committee in 2008 that he had not used performance-enhancing drugs.
Clemens, who pitched for the Boston Red Sox, Toronto Blue Jays, New York Yankees and Houston Astros, entered his plea in U.S. District Court.
Federal prosecutors didn't believe Clemens' testimony to Congress, and they subsequently charged him with making false statements, perjury and obstruction of Congress.
The 48-year-old Clemens had vowed to fight the charges.
At Clemens' arraignment Monday, U.S. District Judge Reggie Walton set an April 5 date for choosing a jury.
If convicted, Clemens could face up to 30 years in prison and a $1.5 million fine. However, a conviction could cause catastrophic damage to his reputation, future earning potential and his chances of getting into baseball's Hall of Fame.
Clemens was being arraigned on three counts of making false statements, two counts of perjury and one count of obstruction of Congress.
He entered the courthouse well before his hearing, which was scheduled for a ceremonial courtroom that seats about 300 people.
After spending the morning in the back rooms of the courthouse, where defendants often go to get their fingerprints and mug shots taken, Clemens and his attorney, Rusty Hardin, went to the main cafeteria, where the pitcher sat at a corner table and had a salad and a bottle of water for lunch.
Clemens was friendly, but declined comment when approached by an Associated Press reporter. Hardin said plans hadn't changed for the hearing, but he wanted to honor the gag order imposed by U.S. District Judge Reggie Walton, who last week ordered interested participants to refrain from making public comments that could have a material effect on the case.
Clemens' early arrival may have been because he wanted to make a quick exit after his hearing is over. The New York Daily News reports that Clemens and his wife, Debbie, planned to fly to Myrtle Beach, S.C., later Monday to play in the Golf.com World Amateur Handicap Championship.
If convicted on all charges, Clemens could face up to 30 years in prison and a $1.5 million fine, though under U.S. sentencing guidelines, he would probably face no more than 15 to 21 months in prison.
All signs point toward him fighting. He came to Congress after being mentioned repeatedly in the Mitchell Report - the damning breakdown of the sport's steroid problem released in 2007.
In front of a House committee the next year, Clemens said: "Let me be clear. I have never taken steroids or HGH." Before his indictment was handed down Aug. 19, Clemens was offered a plea deal that he turned down, and afterward, he showed no signs of backing down.
"I look forward to challenging the Governments accusations, and hope people will keep an open mind until trial," Clemens wrote on Twitter after the indictment. "I appreciate all the support I have been getting. I am happy to finally have my day in court."
His day in court figures to be one of many in the near future for some of baseball's biggest names - now sullied by steroid-related accusations. All-time home run king Barry Bonds is scheduled to go on trial in March on charges of lying to a federal grand jury when he said he never knowingly used performance-enhancing drugs.
At the hearing in front of the House Committee on Oversight and Government Reform, Clemens' former trainer, Brian McNamee, said the pitcher did, in fact, use steroids and HGH. Former teammate Andy Pettitte also told congressional investigators that Clemens told him he had used HGH.
Clemens told Congress that Pettitte "misremembers" the conversation.
All that testimony figures to be rehashed in a trial that could irrevocably tarnish the reputation of one of the most dominant pitchers in history. Over 23 seasons, Clemens recorded 354 wins, 4,672 strikeouts and an ERA of 3.12 - Hall of Fame numbers that might not land him in the Hall of Fame.
Associated Press sports writer Eddie Pells contributed to this story.