Tory shadow cabinet member Gary Streeter, who was fined £1,000 last week for professional misconduct, resigned from the partnership at Foot & Bowden in May, it has emerged.
Streeter, who joined the partnership at the Plymouth firm in 1984, has now become a consultant.
Both Streeter and the firm said the decision was prompted by his forthcoming elevation to the shadow cabinet, which happened in June, rather than the impending Solicitors Disciplinary Tribunal hearing.
"He has not severed his ties with us - he does help us with advice," said senior partner Bill Jones.
At last Thursday's tribunal hearing, Streeter admitted conduct unbefitting of a solicitor. The tribunal heard how he had become involved in a "conflict of interests situation par excellence".
Roger Field for the Law Society said that, in 1991, Streeter advised Lynda Moss on a remortgage application while he was also acting for a company which was in financial difficulties and which she owned with her husband.
He said: "There was clearly a multiplicity of interests here and, had Mr Streeter stepped back and analysed it, he would have realised that he should not have represented her. His position was impossible."
Streeter said he did not believe that Moss had been prejudiced.
"I was following a well-worn path and I did not give it a second thought," he added.