The club announced to the London Stock Exchange that the 65-year-old would oversee the appointment of a chief executive, a role which has been vacant since Craig Mather left.
The club also announced that their annual general meeting would be held on December 19.
Rangers have been without a chairman since Walter Smith stepped down three months ago while Mather left on October 16, days after a group of dissenting shareholders succeeded in a Court of Session bid to force the postponement of the AGM.
The club's statement to the stock exchange read: "The board of Rangers announces that it has appointed David Somers as an independent non-executive director and acting chairman.
"Mr Somers is an honours economic studies graduate and a qualified accountant (Fellow of the Association of Chartered Certified Accountants).
"He spent all his career in fund management and in addition has considerable experience in matters of corporate governance."
A spate of board departures amid an acrimonious power struggle left just two directors on the Rangers PLC board, Brian Stockbridge and James Easdale, before the announcement regarding Somers on Thursday morning. Easdale's brother and business partner, Sandy, is also on the football club board and holds a significant shareholding and proxy voting rights.
Former oldco Rangers director Paul Murray led the court action to postpone the AGM in order that shareholders could consider his bid to be elected to the board along with allies Scott Murdoch, Alex Wilson and Smith's predecessor as chairman, Malcolm Murray.
Rangers are legally bound to hold their AGM before the end of the year and the delay until the week before Christmas could see the current directors bid to fill the board with their allies, although they will all be subject to re-election on December 19.
Another former oldco Rangers director, Dave King, last week admitted failure in his bid to secure a compromise deal between the competing factions.
The club's statement added: "Mr Somers will oversee the current process of appointing a high calibre chief executive officer and further independent non-executive director(s) to form a unified board and provide stability for Rangers. "In order to allow time for the process outlined above to be progressed, the company will hold its annual general meeting on Thursday 19 December."
The statement continued: "Mr Somers will, in accordance with Rangers' Articles of Association, be subject to re-appointment by an ordinary resolution of the shareholders at the AGM."
The statement gave further details of Somers' business background, stating his current directorships on insurance group ACE Europe Life; Europe Arab Bank; a Fujitsu pension plan and TCF Investment Managers.
The statement added: "Mr Somers is not currently beneficially interested in the issued share capital of the company."
Mr Somers released a statement, which said: "It is a huge honour and privilege to be appointed acting Chairman and non-executive Director of Rangers Football Club.
"I know from my visits to Ibrox Stadium - including a number of Champions League games I attended in the past - that the Club has a tremendous fan base.
"Ally McCoist has the players performing well on the pitch so my task now is to strengthen the Board to the level that Rangers Football Club deserves.
"This 141-year-old institution is on the road to recovery and I will do everything in my power to help take this great club back to the very top of Scottish football where it belongs.
"I have a strong background in finance and corporate governance and while there are challenges ahead I am confident they can be overcome and Rangers can rise again.
"Rangers is a global brand and I would urge everyone associated with the club - players, staff, sponsors and most importantly our supporters - to pull together and help take the club forward.
"Ally McCoist and his squad have enjoyed a positive start to the season and we are in a terrific position at the top of the league.
"My priority is to help oversee the recruitment process for a high-calibre Chief Executive and further independent non-executive Directors to strengthen the Board and provide long-term stability for Rangers.
"The Club has confirmed it will hold its Annual General Meeting on Thursday 19 December and we hope to make significant progress before that date.
"I appreciate some supporters have been unhappy with events at the Club in recent weeks and months.
"However, I have taken the position of acting Chairman and non-executive Director as I believe this Club has a bright future and we can achieve great things if we all work together for the good of Rangers.
"It should not be about individuals, it is the Club that is important and I hope everyone with Rangers' best interests at heart can work together in order to take us forward."