Hewat first sought a release from his Waratahs contract in May

The 29-year-old, who has scored 520 points in 40 Super 14 appearances, said the time was right to move on.

The switch comes after a turbulent few months which saw the Australia 'A' cap overhear a Wallabies selector openly criticising him to Lote Tuqiri.

"In my mind I've gone as high as I can go in Australia," Hewat said.

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"It's been a tough process and one that's gone on for a couple of months. I'm very relieved it's all over now."

Hewat initially sought a release from his Waratahs contract in May after being omitted from a 59-man training squad from which Australia finalised their World Cup party.

NSW coach Ewen McKenzie said the Waratahs and London Irish had reached an undisclosed "commercial agreement" over Hewat that would see him move to England after this year's Australian Rugby Championship, but possibly return in future.

NSW coach Ewen McKenzie said: "We are disappointed to lose Peter but we have plans in place to ensure the Waratahs don't lose the special skill set that made him such a valuable player."

London Irish director of rugby Brian Smith said Hewat "is a class act" and believes he will make a "huge impact" on the Guinness Premiership.

"Peter is an out-and-out point scorer who is coming to London Irish at the peak of his career," Smith said.

"We've been looking at signing a world-class goal-kicker for some time and I'm sure our supporters will be delighted by this signing.