Jackson (47), who had represented Illinois in the House of Representatives from 1995 until his resignation in November last year, told US district judge Robert Wilkins on Wednesday he supplemented his income with political campaign funds for seven years.
When Wilkins asked for Jackson's plea, he responded: "Guilty, your honour. I misled the American people."
Prosecutors said they might ask for a five-year prison sentence in the corruption case – the maximum permitted by law – while Jackson's legal team said it might argue for four or less. Sentencing is scheduled for June 28.
"His campaign funds were a personal piggy bank," Ronald Machen, US attorney for Washington, told a news conference.
Jackson, once considered among the nation's most promising black politicians, expressed regret for misusing the campaign money. At one point he turned around to face his family and appeared to mouth the words: "I'm sorry."
"I fully understand the consequences of my actions," Jackson, who dropped out of public view last year and had treatment for bipolar disorder, told the judge.
Waiving his right to a jury trial, he said: "I have no interest in wasting the taxpayers' time, or their money."
Jackson's father, civil rights leader Jesse Jackson, and other relatives and friends sat in the front rows of a Washington courtroom. The elder Jackson declined to answer reporters' questions after the hearing.
Wasted potential
The former congressperson's wife, Sandi, tearfully pleaded guilty at a separate hearing on Wednesday to filing false tax returns that did not report the campaign money as income. She is a former member of the Chicago City Council. She walked into the hearing holding hands with her husband just hours after he also had pleaded guilty.
Jackson signed an agreement with federal prosecutors to end an investigation into his personal finances. Prosecutors said he had cooperated fully with them.
"The guilty plea today is so tragic because it represents such wasted potential. Jesse Jackson Jr had the drive, the ability and the talent to be the voice of a new generation. But he squandered that talent and exchanged that instead to satisfy his personal whims and his extravagant lifestyle," Machen said.
The prosecutors had accused Jackson of shipping a $43 350 man's Rolex watch purchased with campaign funds to his Washington address. He also sent fur capes and parkas purchased with $5 150 in campaign funds from Beverly Hills to the home of an unnamed person, court documents said.
The government had said earlier that Jackson must forfeit tens of thousands of dollars worth of celebrity memorabilia derived from the alleged crimes, including a $4 600 fedora that once belonged to the late pop star Michael Jackson.
Thousands in memorabilia
He must also forfeit $5 000 worth of footballs signed by American presidents, $10 105 in memorabilia from martial arts film star Bruce Lee and $11 130 in Martin Luther King Jr memorabilia. Prosecutors say a final list of the items Jackson must forfeit will be released at his sentencing.
They say he used campaign money to buy $9 588 worth of children's furniture and $1 553 in porcelain items.
The bulk of the money, $582 773, paid for 3 100 purchases on Jackson's personal credit cards. He charged routine items like nightclub tabs, clothing, movie tickets and dining, court papers say. One billing entry in November 2008 lists $5 688 for "Martha's Vineyard Holistic Retreat". Martha's Vineyard is a Massachusetts island that is popular as a summer retreat for the affluent.
"For years I lived off my campaign," Jackson said in court.
In another complicated transaction, Jackson's campaign paid $8 000 to someone identified in court papers as "Person A" for work described as "data entry & cleanup". In fact, prosecutors say, Person A used the money to buy two mounted elk heads for Jackson's congressional office in 2011.
In 2012, Person A sold the elk heads to an undercover FBI agent who was instructed to wire payment to one of Jackson's personal bank accounts.
Jackson's actions add up to conspiracy to commit fraud and give false statements, according to the plea agreement.
Bipolar treatment
Jackson ran for Congress and won at age 30, serving from 1995 until resigning on November 21, citing health reasons and acknowledging he was under investigation by the FBI.
One of Jackson's lawyers, Reid Weingarten, told reporters after the hearing that the court should take Jackson's years of public service into account when he is sentenced. Jackson would not speak to the media but would make his case in court papers, Weingarten said.
Jackson may already be thinking of life after prison.
"There will be another chapter in Jesse Jackson's life, a chapter that brings joy to the people who care about him," Weingarten said.
Jackson disappeared from public view last summer and speculation swirled for weeks about his condition. At first he said he was being treated for exhaustion and in July his doctor said Jackson was receiving intensive care for a "mood disorder".
Jackson eventually was treated for at least six weeks at the Mayo Clinic in Minnesota for bipolar disorder.
Civil rights movement
In accepting Jackson's plea, Wilkins went through a series of questions that are routinely asked of defendants but that took on poignancy because of Jackson's father's career as a civil rights champion: Did he realise he would no longer be able to vote, serve on a jury or own a firearm due to his felony conviction?
Jackson said he did and wiped tears from his eyes.
The elder Jackson was a protégé of Martin Luther King Jr during the civil rights movement of the 1960s and campaigned for voting rights for blacks.
Wilkins's own civil rights history complicated the case. He was a leader of a group of Harvard students supporting Jackson senior's 1988 presidential campaign. Wilkins, who became a judge in 2010, also had appeared on the elder Jackson's CNN television show in 1999 to discuss his successful lawsuit against the state of Maryland for racial profiling of black drivers.
Wilkins offered to step aside from the Jackson cases but neither side wanted him to do so. – Reuters