Sir Geoffrey, 63, was the last remaining member of Mrs Thatcher's original 1979 cabinet.
He served as both chancellor and foreign secretary.
A short statement from Sir Geoffrey was read to journalists by his parliamentary private secretary, David Harris.
There were few details but Mr Harris told reporters Sir Geoffrey had no intention of challenging for the party leadership.
"I have absolute authority from Sir Geoffrey to say that there is no question of his standing against Mrs Thatcher in a leadership election," Mr Harris said.
Labour leader Neil Kinnock said Mrs Thatcher had got what she deserved and had been bitten by the man she had treated as a "doormat".