Robert Kerbeck flopped as an actor. But, as a corporate spy, he gave Oscar-worthy performances.

Working with nothing more than a telephone and a laptop computer, he convinced executives, assistants and receptionists at America’s largest companies to part with secrets worth millions of dollars.

As chronicled in his new book, “Ruse: Lying the American Dream from Hollywood to Wall Street” (Steerforth Press), Kerbeck specialized in getting employment information for headhunters looking to poach workers in the finance, healthcare and tech fields. He deployed a process known as rusing — basically, lying over the phone in order to obtain information under false pretenses — and claimed to be everyone from an auditor at the firm to a compliance officer.

“Let’s say the two top traders at a Wall Street firm are managing directors,” Kerbeck, 58, told The Post. “They make a ton of money and would be expensive to hire. But if the number-three broker is an associate, he’s a rock star who’s unknown and won’t cost you the farm. I specialized in finding that guy for the headhunter.”

Describing himself as having once been “the world’s greatest corporate spy,” Kerbeck had no qualms about being outlandish.

“The funniest ruses were the ones in which I put on phony accents,” he said. “I was particularly good at sounding German.” Speaking in the voice of a harried man from the Fatherland, he said, “I am calling from Frankfurt. The regulators are breathing down our necks. I need everyone in the department and their internal rankings” – i.e., their performance standings.

If a suspicious assistant asked why he needed it, Kerbeck stayed in character and said, “As you say in America, killing all za birds with one stone.”

At the turn of the 21^st century, when companies was panicked about Y2K shutting down the world, Kerbeck pretended to be an IT worker who needed to know how much money certain workers generated. Not wanting to be responsible for crippling their companies, employees spilled the confidential information he requested.

He also made outrageous promises to vulnerable executives. As explained in the book, Kerbeck sometimes claimed to be calling from the tax department, looking for people that an outside vendor — say, Price Waterhouse — could take to Knicks and Rangers games. Kerbeck received employee names, numbers and floors on which they worked.

The son of a car salesman, Kerbeck went from his hometown of Huntingdon Valley, Penn. (where he went to high school with CIA operative Valerie Plame), to pursue a career in acting. That brought him to New York in the late 1980s, where he had some success performing in the well-received off-Broadway drama “Bovver Boys.” He was invited to participate in a reading at the home of Joanne Woodward and Paul Newman, appeared in a David Fincher-directed MTV video for a band called the Hooters and, Kerbeck writes, was hit on by Kevin Spacey (Kerbeck rebuffed him).

Like most struggling actors, Kerbeck needed a source of revenue. A friend introduced him to a woman who hired underemployed actors to do spy work for corporate clients. “Every company uses spies,” he said.

In the early 1990s, he moved to Los Angeles and divided time between freelance rusing and assorted acting gigs. There was an appearance on “Sisters” with George Clooney in the early ’90s. “I sensed desperation and disappointment in him,” Kerbeck said. “He had booked six pilots that didn’t go and everything was riding on [Clooney’s new NBC show] ‘ER.’”

Then there was an O.J. Simpson exercise video, which Kerbeck was participated in as a background workout buff because he got to keep the gym shorts and sneakers.

“I’d been using shoe glue to cover the holes in mine,” he writes.

By the late 1990s, after a failed pilot of his own called “NightMan,” Kerbeck’s acting career sunk but the spy business soared. Between ’02 and 2008, he claims, he went from making $204,000 per year to more than $2 million. Then the stock market crashed and the bottom fell out of his spy game.

Just as money got tight, one of Kerbeck’s executive-recruiter clients offered him a deal that seemed too good to be true: He’d buy the rusing company and hire Kerbeck to be a headhunter, which he welcomed as a more legitimate profession.

However, Kerbeck said, “I went from being the ruser to the rusee. They promised to pay me back for office rent, which they never did. They stiffed me on my bonus, didn’t buy the company and stole my best employee.”

Kerbeck left and eventually turned to writing and day-trading stocks but, he added: “Corporate spying still works … it is down-and-dirty, alive and well.”