The 31-year-old British Superbike frontrunner is stepping up to MotoGP with Paul Bird Motorsport's new self-built CRT chassis this season.
Laverty said that even after BSB champion Shane 'Shakey' Byrne turned down the seat, he did not imagine he would be top of the list of alternatives.
"I know I wasn't first choice for the ride, Shakey was," Laverty told the MotoGP website.
"And when he turned it down I was actually surprised to get the call, but it was a nice surprise."
He added: "Honestly it's something I never expected I'd get the opportunity to do.
"I'm a realist I reckon, and once you pass your mid-20s you think that if you haven't got to GP by then, then it's not going to happen, so I kind of thought that if I ever got a shot at a world championship that it would be in World Superbike, so it's nice that things have changed."
PBM had a tough 2012 season with James Ellison on its Aprilia. Yonny Hernandez will continue to ride that bike in 2013 while Laverty takes the new PBM design.
Laverty's bike will run the spec ECU that will be mandatory from 2014. He hopes this will ensure strong support from Aprilia, which dominated CRT with its lead squad Aspar last year.
"They seem happy to let the team work on the new project and work on the new electronics," said Laverty.
"Aprilia will have in mind that from 2014 they are going to have to run the Magneti Marelli system, so it's useful for them to have another team using it as it gives them a lot of data.
"They seem happy to help the team sort out the engine management with the Magneti Marelli system so overall I think the relationship with Aprilia is quite good, so hopefully we'll be even, or as close to even as possible to them."
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