Embattled former Probation Commissioner John J. O’Brien filed for his state pension on New Year’s Eve, the same day he abruptly resigned his $130,000 post rather than face a disciplinary hearing that could have prevented him from receiving his pension.

O’Brien, whose termination hearing was set to take place tomorrow, will get a pension estimated at $4,000 a month for the rest of his life and his beneficiary, likely his wife, will receive $2,600 a month after his death.

David Kibbe, a spokesman for State Treasurer Tim Cahill, said it will take about 60 to 90 days before a final determination is made on O’Brien’s pension request.

O’Brien, 53, had been suspended with pay in May after a series by the Boston Globe Spotlight team and reports by other media, including CommonWealth magazine, portrayed the Probation Department as an agency awash in political patronage hires made in exchange for budget support.

The Supreme Judicial Court ordered O’Brien’s termination hearing after a report by an independent counsel alleged the commissioner regularly approved job candidates based largely on their connections to powerful politicians. The report by Paul F. Ware has been turned over to various criminal and civil agencies, including the US Attorney’s office, the Attorney General, the State Ethics Commission, and the state Inspector General, all of which have launched investigations of their own.

If O’Brien is convicted of criminal charges, he could lose his pension altogether. Paul Flavin, O’Brien’s attorney, issued a press release announcing O’Brien’s resignation last Friday saying his client did nothing criminal and did no more than any other state agency head in hiring recommended candidates.

In resigning, Flavin said O’Brien was avoiding a rigged hearing that would have been run by Robert Mulligan, the chief justice of Administration and Management. “Commission O’Brien’s due process rights have been violated and it is inconceivable that, under these circumstances, he will receive a fair hearing before Chief Justice Mulligan regarding the allegations contained in the Ware Report,” Flavin wrote. 

According to the pension application filed by O’Brien, the former commissioner was employed by the state court system since July 1980, working his way up through the ranks until he was named commissioner of probation on Jan. 1, 1998.

O’Brien’s monthly retirement check is based on his three highest earning years, which would be his last three as commissioner. O’Brien has opted to have a reduced pension so a beneficiary can continue to receive a monthly check after his death.

According to a calculator on the retirement board’s website, O’Brien would be eligible to collect an annual pension equal to about 40 percent of his $130,000 salary based on his age and his length of service.