The pair will appear on the panel alongside the returning Amanda Holden when the series comes to ITV in 2011. Simon Cowell will not be present for the auditions but will reprise his role for the live stages.
Elaine Bedell, ITV Director of Entertainment and Comedy, said: “Michael has established himself as one of the biggest names in comedy and entertainment in this country and, as someone who made his big breakthrough on the Royal Variety Performance, he knows exactly the pressures facing the acts on Britain’s Got Talent."
Of his new role, McIntyre said: “I'm a massive fan of Britain's Got Talent and am extremely excited to be a judge on the new series. I was so thrilled when Simon Cowell asked me that I immediately wanted to run in to Ant and Dec's arms to celebrate!”
Actor and television personality Hasselhoff previously served on the judging panel for NBC series America's Got Talent from 2006 to 2009.
“As an actor, singer and producer, David Hasselhoff has been immersed in show business for many years," said Bedell. "Alongside Michael, Amanda and of course Simon Cowell, he is a great addition to the judging panel for 2011.”
Ant and Dec will continue to present the hit show.