Meet Al Sharpton, “Confidential Informant No. 7.”

The longtime agitator, civil-rights activist and TV host was exposed Monday as an alleged former key FBI informant whose tips helped take down some of the biggest names in New York Mafia history.

The Rev. Al launched his sensational secret life as a paid mob snitch in the mid-1980s, pressured to cooperate after being ensnared in a developing drug sting, according to a bombshell report by thesmokinggun.com.

As “CI-7,” the then-portly Harlem leader would tote a customized Hartmann briefcase equipped with an FBI bug to hobnob with members of some of the city’s most notorious crime families, the site said.

Sharpton’s main job was to dig dirt on the Genovese crime family, according to sources and court documents.

He was so good at “playing dumb’’ that he wound up helping to bring down such names as Venero “Benny Eggs’’ Mangano, Dominick “Baldy Dom’’ Canterino and even the muttering “oddfather” of Greenwich Village, family boss Vincent “Chin’’ Gigante, the site said.

He was a “very reliable informant, and his information ‘has never been found to be false or inaccurate,’ ” the report said, quoting a 1986 court document.

While it was known that Sharpton had spied for the FBI on music- and sports-promotion figures, the new data said he also extracted juicy information from wiseguys.

The feds later used the dirt to obtain warrants to bug key Genovese spots.

Because of Sharpton’s undercover work, listening devices were surreptitiously installed in two crime-family social clubs, including Gigante’s Village headquarters, three cars used by Mafiosi and more than a dozen phone lines, the site said.

Information gleaned from those bugs then helped nail the mobsters.

One of Sharpton’s main unsuspecting founts of useful information was Joseph “Joe Bana’’ Buonanno.

During 10 face-to-face chats between the pair, “Joe Bana just gave him a whole insight into how ‘Chin’ and [music-industry honcho] Morris [Levy] operated,’’ said an NYPD source with the joint FBI-Police Department “Genovese Squad.”

Before his rapt audience of one, Buonanno expounded on the mob’s past extortions and death threats.

He even allegedly revealed to Sharpton a few not-so-flattering details about his boss, Gigante, who for years pretended he was crazy by shuffling around the West Village in a bathrobe to escape prosecution by the feds.

Buonanno told Sharpton of the godfather’s purported illiteracy and the fact that he “hates everyone not Italian,” the site said.

The mob soldier even detailed how Gigante “was present” at the hit of Genovese captain Thomas “Tommy Ryan’’ Eboli, to “make sure it was done right,” the site said.

Still, while Sharpton had the gift of gab and got Buonanno to unwittingly spill his guts, the mob soldier snottily referred to the preacher as “a nose picker’’ behind his back, an associate told the site.

Both Buonanno and Gigante are now dead.

The revelation of Sharpton’s involvement with the feds couldn’t have come at a more embarrassing time.

Sharpton is set to convene the annual convention of his National Action Network in New York this week — with Mayor Bill de Blasio cutting the opening-ceremony ribbon Wednesday and President Obama flying in to give the keynote address Friday.

Sharpton, in an interview with The Post on Monday, didn’t deny that he cooperated with the FBI — but said the thesmokinggun.com report was the equivalent of a mob hit.

“It’s crazy. If I provided all the information they claimed I provided, I should be given a ticker-tape parade,” said Sharpton, 59, who now regularly rubs elbows with Obama and his wife, Michelle, Attorney General Eric Holder, congressmen and other national leaders.

“What did Al Sharpton do wrong? Eliot Spitzer did do something wrong, and he got a TV show,” said the Rev. Al, referring to the hooker-loving former governor.

Sharpton is currently the host of MSNBC’s “PoliticsNation.’’ He regularly wraps up one segment by pointing a finger at the camera and yelling, “Nice try, but we gotcha!”

He denied being paid to snitch and said he never carried a briefcase with a listening device.

He insisted that if he did cooperate with the feds, it was because he’d been threatened by a mobster while working with black concert promoters.

“The article is embellished. The real story is I told the FBI about being threatened because I was a civil-rights leader helping black concert promoters,” Sharpton said.

He griped that the report was simply an attempt to “muddy’’ him before this week’s NAN convention.

A Sharpton confidante who’s known him for decades was caught off guard by the extent of the activist’s alleged dealings with the FBI.

“Holy s- -t,’’ the source said. “This comes out of left for me. I’m actually driving off the road.’’

But veteran Democratic political consultant George Arzt said the report is more likely to boost Sharpton’s standing with the public rather than hurt it.

“This is just going to add to his luster of being a character,” Arzt said. “It does raise questions about an anti-establishment guy cooperating with the FBI. But now he is establishment.”

Sharpton was considered prime fodder as a mole for the FBI’s Mafia unit because of his already-existing connections to the underworld, the site said.

For example, he knew Genovese soldier Joseph Pagano, who was involved in entertainment-industry schemes for decades, allegedly controlled “Rat Pack’’ singer Sammy Davis Jr. and once even “lost a big roll [of money] to Dean Martin and Frank Sinatra,’’ FBI sources said.

Sharpton allegedly told the feds he had an in with Pagano because he’d introduced him to boxer Muhammad Ali and his reps.

In trying to nail the Genovese Mafiosi with Sharpton’s help, the feds embarked on their bugging scheme — sometimes producing hilarious results, the report said.

At one point, the Genovese Squad tried to wire mobster Dominick Canterino’s Cadillac in front of his Gravesend, Brooklyn, home.

An agent broke into and hot-wired the car to briefly drive it off to plant the bug before returning it.

“Piece of cake,’’ he radioed to fellow agents down the block.

“You’re burned!” an NYPD detective shouted back a minute later, as he spotted Canterino watching the agent drive away with his car.

“In retrospect, it was like a Keystone comedy,’’ chuckled a former FBI agent who was there that day. “But it wasn’t so funny when it occurred.”

Canterino has since died.