The Emmy-winning actress, 56, could face prison time after she admitted to participating in the scam, in which authorities say parents bribed coaches, rigged entrance exams or both to game the admissions system.
Huffman pleaded guilty in a US court to paying an admissions consultant US$15,000 to have a proctor correct her older daughter's answers on the SAT.
She also considered going through with the plan for her younger daughter before ultimately deciding not to, authorities say.
She arrived at court holding the hand of her brother Moore Huffman Jr and did not say anything to journalists. In court, she sat flanked by her lawyers while her brother watched from the front row. Her husband, actor William H Macy, didn't attend.
She stood with her hands clasped in front of her and responded, "Yes, your honour," when asked whether she understood the charges.
Sentencing was set for September 13. Prosecutors are seeking four to 10 months behind bars.
Because she agreed to plead guilty, prosecutors said they would recommend four months in prison, but the judge could also choose not to put her behind bars at all.
Huffman apologised in a statement last month and said she will accept the consequences. She said she "betrayed" her 18-year-old daughter, who was not aware of her plan.
"This transgression toward her and the public I will carry for the rest of my life. My desire to help my daughter is no excuse to break the law or engage in dishonesty," Huffman said.
Investigators have said Macy, 69, was with her when admissions consultant Rick Singer explained how he could arrange for the cheating because he "controlled" a test centre.
Both Huffman and Macy agreed to the plan, authorities say, but Macy has not been charged. Prosecutors have not explained why.
California businessman Devin Sloane also pleaded guilty to paying US$250,000 in bribes to get his son into the University of Southern California as a fake water polo recruit.
Authorities say he gave a total of US$250,000 to Singer's sham charity and the USC women's athletic programme to have his son designated as a water polo recruit even though he didn't play the sport.
Officials say Sloane even bought athletic gear online and worked with a graphic designer to create a bogus photo of his son playing the sport for the teen's application.
Huffman and Sloane are among 14 parents who agreed to plead guilty in the biggest admissions scandal ever prosecuted in the US, known as "Operation Varsity Blues."
The scandal involving prestigious schools across the country has also embroiled prominent college coaches.
The parents are accused of paying Singer to bribe coaches in exchange for helping their children get into schools as fake athletic recruits.
Singer also paid off entrance exam administrators to allow someone else to take tests for students or fix their answers, authorities say.
Huffman was among the stars of the popular series Desperate Housewives, which won her an Emmy Award in 2005. Huffman was also nominated for an Oscar for playing a transgender woman in the movie Transamerica.
Experts differ on whether Huffman's swift acceptance of responsibility will leave her with an acting career.
After Huffman agreed to plead guilty, Netflix officials said a film starring her, Otherhood, would not be released as planned in April and a new date would be determined.
A limited series featuring Huffman on the Central Park Five case is expected to debut this month.
Some parents have decided to fight the charges.
They include fellow actress Lori Loughlin and her fashion designer husband, Mossimo Giannulli, who have pleaded not guilty to paying US$500,000 in bribes to get their daughters into the University of Southern California as crew recruits even though neither of them is a rower.
Loughlin and Giannulli, who are also charged with money laundering conspiracy, have not publicly commented on the allegations.
Singer has pleaded guilty to charges including racketeering conspiracy. He began working with authorities last year and secretly recorded his conversations with Loughlin, Huffman and other parents in the hopes of getting a lenient sentence.