The son of a former FDNY commissioner arrested for defecating on a stranger’s lawn furniture during a drunken night in New Jersey is back on the job, The Post has learned.

Since entering a plea deal in which he admitted to “littering,” Joseph Cassano, son of ex-commissioner Salvatore Cassano, “has returned to work” as a probationary firefighter, the FDNY said Friday.

Cassano, 28, served a routine 30-day suspension after his bust last month on criminal trespass and criminal mischief charges. Police said he pooped on the lawn chair and sidewalk at a Lake Como, N.J., residence before stumbling into the garage and passing out drunk.

In the July 10 plea deal, the criminal charges were dropped, said Cassano’s lawyer Aidan O’Connor, a former assistant US attorney.

Cassano admitted violating two municipal ordinances – noise and littering, O’Connor said. He paid a $4,000 fine.

“This was a momentary lapse. It’s not what it seems,” O’Connor said.

Cassano was trying to redeem himself after resigning in disgrace from his job as a city EMT in 2013 when The Post exposed his racist and anti-Semitic comments on Twitter.

The city rehired him as an EMT in 2015 and promoted him to firefighter in April.

The FDNY would not say whether Cassano violated department rules, or if he faces further penalties.