For the two counts, the maximum sentence is 23 years in prison and a $500,000 fine, but Mulgrew likely will face a sentence that could range from probation to two years behind bars.
No deal was struck for a precise sentence. Nor was there any requirement that Mulgrew cooperate further with prosecutors.
The sentence will be up to U.S. District Judge C. Darnell Jones 2d, who set the sentencing date for Dec. 16.
Mulgrew still faces another criminal case. He is among six current or former Traffic Court judges expected to stand trial early next year on federal charges of fixing tickets. Three other former judges have pleaded guilty in that case.
While Mulgrew on Thursday pleaded guilty to only one count of evasion, he agreed to pay taxpayers back for evading federal taxes from 2006 to 2010. The sum owed is still to be negotiated with prosecutors, though they have said previously that he dodged $80,000 in taxes during those years.
After the plea, Assistant U.S. Attorney Paul L. Gray, who led the investigation, called Mulgrew's thievery "completely unwarranted, unnecessary, . . . and offensive."
Brian J. McMonagle, Elizabeth Mulgrew's lawyer, had told the jury Wednesday that she had played no role in any of the tax returns beyond signing them.
After the plea Thursday, McMonagle called the day "bittersweet."
He added: "I have enormous respect for Bob for standing up for his family."
Gray told the jury Wednesday in opening remarks that Mulgrew had ripped off the Friends of Dickinson Square nonprofit organization by pocketing its money or hiring relatives and political insiders for low-show jobs. He was the vice president of the organization, which was formed to clean up the park near Fourth and Tasker Streets.
Among other abuses, the government said, Mulgrew billed the nonprofit for leases on pickup trucks that served mostly as his personal vehicles, as well as for an $827 camera, extermination services, and cigarettes.
Gray said Mulgrew cheated on taxes by simply not reporting the money he stole from the Dickinson Square group. Mulgrew also sheltered income with bogus tax deductions, falsely claiming, for example, that his wife had had driven 236,000 miles selling real estate in South Philadelphia - a figure that Gray said was inflated by a factor of 30.
Joining Gray in the investigation were IRS special agent Laura Capra, FBI special agent Jason Blake, and forensic accountant Cindi Fusco, a staffer with the U.S. Attorney's Office in Philadelphia.
Mulgrew has been immersed in South Philadelphia politics and civic life for many years.
His lawyer, Angie Halim, told jurors Wednesday that Mulgrew and his wife had lived in the same house for 37 years, raising four children now aged 27 to 34.
After hurting his back and knees as a longshoreman, Mulgrew worked in the neighborhood office of former State Sen. Vincent J. Fumo for about 10 years until Fumo fired him in 2002 for refusing to take off a political sticker touting Ed Rendell for governor at a time when Fumo was backing Bob Casey, now a U.S. senator.
Mulgrew then went to work as a union official with Local 98 of the electrical workers union, a local led by Fumo enemy John J. Dougherty. The union poured $120,000 into Mulgrew's successful 2007 campaign for Traffic Court.
As one of seven elected Traffic Court judges, Mulgrew ruled on 123,000 moving violations since 2008, records show. This made him one of the court's busiest judges until he was suspended with pay after his indictment a year ago for ripping off the nonprofit.
His was the first of a series of indictments that fueled public and political outrage that led Gov. Corbett and the legislature to abolish Philadelphia Traffic Court in January. As a result of that legislation, Mulgrew's position will expire with the end of his six-year term at the close of 2013.
Prosecutors said the state grants in question were garnered for the nonprofit by State Rep. William Keller, the Democrat who represents the area in the legislature's lower chamber.
A top Keller aide, Lorraine DiSpaldo, 58, pleaded guilty in April to joining with Mulgrew in the scheme.
Jones has set her sentencing for Nov. 25.
Contact Craig R. McCoy at 215-854-4821 or email@example.com or follow @CraigRMcCoy on Twitter.
Staff writer Mark Fazlollah contributed to this article.