A former top aide to Rod Blagojevich pleaded guilty today to wire fraud, admitting he discussed having his the-boss appoint an adviser to President Obama to the U.S. Senate in exchange for financial benefits for the ex-governor.

As part of his plea deal in federal court, former chief of staff John Harris, 47, of Chicago, has agreed to act as a witness against Blagojevich. Today's plea makes Harris the first of those indicted in the same case as Blagojevich to officially turn on his old boss. The government will recommend Harris receive 35 months for his crime. Harris' lawyer said after court he'll seek far less.

Harris was arrested along with Blagojevich last December. Almost immediately, he agreed to cooperate with federal investigators. Although his name appeared throughout the 75-page indictment handed down in April, he faced just one count of wire fraud.

The charge involves phone discussions Harris had with Washington D.C. advisors regarding landing financial benefits for Blagojevich in exchange for appointing senior adviser Valerie Jarrett to the U.S. Senate seat vacated when Obama became president.

Jarrett is not accused of wrongdoing and Obama, in a report released last year, said Jarrett did not take part in any quid pro quo discussions with Blagojevich.

Harris' attorney, Terry Ekl, has said Harris had done nothing to financially benefit himself. His cooperation has been crucial to giving prosecutors a roadmap to Blagojevich's final days in office.

Blagojevich's longtime pal and former chief of staff, Lon Monk, who was pivotal in the ex-governor's fund-raising efforts, is also expected to enter a guilty plea later this month.