Jeremy Wray has ended his four-year association with Swindon Town after being replaced as chairman.
Wray said his departure was a "specific request" of majority shareholder Andrew Black and he has declined to accept a new role on the board.
Sir William Patey, former British ambassador to Afghanistan, has been named as his successor.
Wray took over from Andrew Fitton in April 2011 and has played a major part in their recent revival.
He orchestrated the appointment of Paolo Di Canio, who lead the club to the League Two title last season, and has publicly backed his manager during the Italian's eventful tenure.
Swindon currently occupy the final play-off place in the League One table but were served with a Football League transfer embargo last week, after they exceeded the set wage and fee limit.
Di Canio voiced his anger at the embargo, saying the board have reneged on their ambition of achieving back-to-back promotions.
But he was quick to praise Wray following Town's 2-2 draw with Coventry on Saturday, describing him as "the best chairman a manager could have".
Wray said in a statement: "Having met Sir William, I am confident he will bring great value to the board, but, after much reflection, I have concluded that it would be inappropriate to accept the offer to remain on the board and as such intend to terminate my engagement with the club.
"When I agreed to take over as chairman it was on the understanding that the board would confirm the appointment of Paolo Di Canio as manager and would commit to a three-year plan to support him, his management staff and players in the attempt to achieve promotion back to the Championship.
"I am proud to have overseen significant progress towards this goal and privileged to have stewarded the club through one of the most exciting periods in its history."
Patey has previously served as British ambassador to Afghanistan, Iraq and Saudi Arabia.
He said: "I am delighted to become chairman of Swindon Town at such an exciting time. I look forward to working with Paolo, the board and the whole club so that success on the pitch can continue and take the Club back to the Championship.
"In addition, my task will be to secure new investment to support the programme of ground redevelopment and to co-ordinate the execution of the club's longer term strategic plans."