"Guilty, your honor," Jackson responded to US District Judge Robert Wilkins after looking back at family members in the courtroom, including his father, civil rights activist Jesse Jackson.
"I used monies that should have been used for campaign purposes," Jackson acknowledged to the judge.
When Wilkins asked if he realized that the guilty plea meant giving up the right to a trial, Jackson responded: "I have no interest in wasting the taxpayers' time or money."
Wilkins set sentencing for June 28.
Jackson's wife, former Chicago Alderman Sandra Stevens Jackson, had her own court appearance scheduled for a few hours later. She was expected to plead guilty to filing false tax returns.
Jackson pleaded guilty to one count of conspiracy to commit wire fraud, mail fraud and false statements. That charge carries a maximum of five years in prison and a $250,000 fine, but Wilkins noted that prosecutors and defense attorneys appeared to recommend a lighter sentence.
However, Wilkins said he was not bound by sentencing guidelines, telling Jackson: "The bottom line is, I don't know what sentence you're going to get and you don't know what sentence you're going to get."
Jackson's lawyer, Reid Weingarten, told reporters after the hearing that he would mount a strong legal case for a fair sentence, noting his client is the father of two young children and has health issues that influenced his behavior.
Last year, Jackson dropped out of public sight to get treatment for mood disorder and other problems.
"It turns out that Jesse has serious health issues," Weingarten said. "Many of you know about them. We are going to talk about them extensively with the court and those health issues are directly related to his present predicament. That is not an excuse. That is just a fact. And Jesse has turned a corner there as well."
Neither Jackson nor his wife spoke to reporters when they arrived at the courthouse in Washington.
Last week, prosecutors filed charges against the couple in separate criminal informations, which are used when parties strike plea agreements.
The documents say the former Democratic congressman from Illinois misused about $750,000 in campaign funds from August 2005 through approximately July 2012.
According to court documents, Jackson's campaign credit cards were used for $582,772 in personal expenditures. Jackson's purchases included a gold-plated men's Rolex watch costing more than $43,000 and almost $10,000 in children's furniture.
As part of the plea agreement Jackson, 47, will have to forfeit the $750,000 in improperly used funds and assorted memorabilia that prosecutors said he bought with campaign cash.
The items include two hats belonging to the late singer Michael Jackson costing more than $8,000; a $5,000 football signed by U.S. presidents; and memorabilia involving the Rev. Martin Luther King Jr., Malcolm X and martial artist Bruce Lee.
Jackson issued a statement through his attorneys Friday that said, in part, "I offer no excuses for my conduct and I fully accept my responsibility for the improper decisions and mistakes I have made."
Jackson's wife is not mentioned by name in the document outlining misuse of campaign funds.
But there are references to her as "Co-Conspirator 1," a former consultant and later the manager of Jackson's re-election campaign. According to the court documents, "Co-Conspirator 1" bought $5,150 worth of fur capes and parkas and had them shipped from Beverly Hills, Calif., to Washington.
Sandra Jackson faces up to three years in prison and a $250,000 fine for one count of filing false tax returns from 2006 through 2011.
Jesse Jackson Jr. had served in Congress since 1995. His name came up during the investigation of former Illinois Gov. Rod Blagojevich, linked to allegations that Blagojevich attempted to sell the US Senate seat vacated by Barack Obama when he became president.
No charges were filed against Jackson, but the House Ethics Committee decided to look into whether Jackson or an associate offered to raise a large amount of money for Blagojevich in exchange for Jackson getting the Senate seat.
Jackson dropped out of sight last spring and his office later said he was being treated at the Mayo Clinic for a mood disorder, depression and gastrointestinal problems. He was re-elected in November but resigned a few weeks later.
His father recently said his son was "taking his medication and handling his challenges."
Sandra Jackson resigned her position as a Chicago alderman in January.