Darren Greenfield and his son Michael, a former NSW branch assistant secretary, had been accused of accepting bribes from a building company for preferential treatment from the union and access to contracts, spanning as far back as 2018.
On Tuesday at the Downing Centre Local Court, the senior Greenfield pleaded guilty to two counts of receiving or soliciting a corrupting benefit, with two other counts of the same charge withdrawn in a deal with prosecutors.
His son pleaded guilty to one count of receiving or soliciting a corrupting benefit along with another count of wilfully or corruptly making a false declaration.
Both have had their bail extended before sentencing on May 26.
The charges were first brought in 2021 and became the subject of intense interest in 2024 after an investigation by Nine newspapers into alleged union corruption.
The CFMEU's construction arm was put into administration after a move against union leadership by the Albanese government following the allegations.
The Greenfields' lawyer Paul McGirr noted the matter had "dragged on and on" for years, and said the plea deal brought "mixed feelings" for his clients.
"It's been well documented their capacity to fund a full-blown legal defence was hampered by the CFMEU's administration," he told AAP.
"They accept their involvement with certain elements of it and this case has been going since 2018, they've been on bail with strict conditions for a long part of that and they just want to put it behind them."
Bail conditions had forced the Greenfields to report to police stations daily and not leave NSW, Mr McGirr said.
Darren Greenfield's employment with the CFMEU was terminated on the same day the union was forced into administration, after Michael had resigned as the union's NSW branch assistant secretary several weeks earlier amid media scrutiny.