Gorrie's move, which is seen as a significant coup for Simpson Thacher, will give the US firm a UK legal capability in acquisition finance for the first time.
At present, the department contains just one US-qualified partner, Jay Ptashek, who was made up a year ago.
While both firms deny the threat of clients moving from A&O to Simpson Thacher, the US firm's relationship with JPMorgan Chase and KKR, both of which use the two firms, will undoubtedly be strengthened.
Walter Looney, London managing partner at Simpson Thacher, admitted that the firm had tried to court Gorrie, as well as a handful of other UK partners, three years ago. However, at that point, said Looney, Gorrie “was not ready to move”.
But earlier this year talks were reignited, resulting in Gorrie's resignation from A&O last week.
Gorrie has practised at A&O for 15 years and was the first assistant to work with Tony Keal, the highly-rated head of acquisition finance at the firm. Both Keal and Gorrie were instrumental in establishing the department.
Keal said he was aware that Gorrie had been assessing his career. “He had never expected to be in a single job for the whole of his life,” he added.
Gorrie was unavailable for comment.