David Somers has resigned as Rangers chairman only days before his future in the position was due to be voted on by shareholders.
The move was confirmed in a statement to the Stock Exchange on Monday.
An extraordinary general meeting is being held at Ibrox on Friday, when the future of the current board is to be decided.
It is unclear if chief executive Derek Llambias and finance director Barry Leach will also go before Friday.
The Rangers Supporters Trust (RST) says it is "delighted" at Somers' resignation, describing him as "inept and embarrassing".
It has also announced that it has been given the proxy vote for the shares owned by former Rangers manager Walter Smith and now claims to have voting rights for 6.3% of the shareholding.
The EGM was called by shareholder Dave King, who has tabled resolutions aimed at ousting the current board and appointing himself, Paul Murray and John Gilligan in their place.
Somers, 66, had been chairman since October but has faced numerous calls to step down by fans who have been protesting for change.
He said in a statement: "I have worked in the City of London, the world's greatest financial centre for decades and enjoyed considerable success.
"When I was approached about the chairmanship of Rangers, friends warned me that the world of football has different rules and codes of behaviour.
"I now know that is a gross understatement.
"I am a non-confrontational man and have always tried to bring harmony to boardrooms and with stakeholders.
"At the risk of antagonising my army of critics, I would point out that Rangers managed to pay its bills and avoid going under during my tenure.
"These critics might not agree with how we achieved this.
"I look forward to alternative solutions from whoever is running the club in the future.
"Despite the personal attacks on me from various sources, I genuinely wish the club the very best in the future and I am confident that with such a passionate and vociferous fan base they will be restored to their former glories."
Director James Easdale last week resigned from the board, giving his reason as a lack of support from the club's fans.
In a damning statement, the RST said Somers' comments were "entirely in keeping with his behaviour" during his tenure.
It said: "His lack of ambition or ability, rampant self interest, contempt for shareholders and fans, and disastrous dearth of understanding of the position of responsibility he held will be his legacy.
"He will be remembered as one of the most inept and embarrassing chairmen of our wonderful sporting institution."
And the fans' group has called for the remaining directors, Llambias and Leach, to "follow Mr Somers out of the door".
"Mr Leach should have resigned when he made disparaging comments about major shareholders in a meeting with fans," said the RST statement.
"This amounted to gross misconduct in our opinion and in any normally operating business he would no longer be in position. He should be suspended and subject to disciplinary procedures after the general meeting.
"Mr Llambias has serious questions to answer over the recruitment process which saw him appointed as chief executive. Not least whether the inaccurate information which appeared in his bio on the Rangers website, and was circulated to shareholders, formed part of the information relied on to support his application.
"His ham-fisted attempt to use legal threats to silence legitimate criticism from the outgoing Fan Board has further alienated supporters. Taken together we believe these make his position untenable. He should also be suspended and subject to disciplinary procedures after the general meeting."
On the subject of Smith passing his voting right to the RST, a spokesman said: "Obviously we are delighted that Walter has agreed to proxy his shares to us.
"We are sure he shares our hope that things are about to change for the better."