Less than halfway through his decade-long assignment, court-appointed FDNY diversity monitor Mark Cohen has already piled up more than $10 million in legal bills, The Post has found.

The former white-collar prosecutor’s startling tab has shot up each year since Brooklyn federal Judge Nicholas Garaufis handed him the lucrative gig in 2011, according to court records.

Cohen gave taxpayers a $1,601,292 bill for 2012, $1,847,733 in 2013, and $3,175,358 for 2014, records show.

Cohen billed a total of $3,766,661 in 2015 — bringing his grand total to $10,391,044 for four years of work.

The lawyer submits bimonthly invoices to Garaufis for approval, with his most recent bill charging $658,342 for November and December.

If he worked seven days a week, Cohen’s bill would tab up to $10,966.67 a day. If the attorney and his staff took weekends off, the daily haul would be $16,000.

Cohen’s bimonthly bills have been bloating significantly over the past four years, records show.

In 2012, they averaged $212,292. They rose to $307,955 in 2013, climbed to $529,226 in 2014 and topped out at $627,776 for 2015.

Cohen’s most recent bill even included a $33,577 charge to prepare a 32-page status report.

The financial inferno is only beginning to rage, as Cohen still has six more years of billing until the 10-year assignment ends.

The lawyer is tasked with boosting diversity in the FDNY. His appointment came after a 2007 federal lawsuit against the city on behalf of minority candidates who claimed they suffered from systematic hiring discrimination.

The Bloomberg administration fought the case for years before Mayor Bill de Blasio agreed to settle for a whopping $98 million in 2014.

Stunned by Cohen’s mammoth invoices, former Mayor Bloomberg’s corporation counsel Michael Cardozo skewered the payments in 2012 and demanded that Cohen corral his costs.

“While the court monitor offered reassurance that it was his aim to be efficient and cost-effective, there appears to be a great deal of wastefulness in the approach to this case thus far,” he wrote to Garaufis in 2012.

Cohen’s average bimonthly 2015 invoices were more than double that amount.

But despite the mushrooming costs, de Blasio’s city lawyers haven’t raised any objections.

“The bills reflect the substantial investment of time by the monitor and his team,” a city Law Department spokesman told The Post. “There are weekly conference calls and frequent meetings with the parties to discuss initiatives undertaken by the FDNY to address issues raised in the litigation.”

Cohen did not return a call for comment.