Jackson waived his right to a trial in a Washington, D.C., courtroom. Under a plea deal, the former Illinois congressman could get nearly five years in prison when sentenced in June.
He told U.S. District Judge Robert L. Wilkins, "I've never been more clear in my life" in his decision to plead guilty.
"Sir, for years I lived off my campaign," Jackson said. "I used money I shouldn't have used for personal purposes."
Jackson's father, civil rights leader Jesse Jackson, was at the courthouse to watch the proceedings. He said nothing to the media and sat expressionless in the front row.
His wife Sandra also agreed to plead guilty to a charge of filing false joint federal income tax returns. According to court papers, his wife spent $5,150 on fur capes and parkas.
When prosecutors charged the couple last Friday, the ex-congressman said he fully accepts the responsibility for the improper decisions and mistakes he has made.
The Associated Press contributed to this report.