Ms Markland will also be a member of the corporate governance and nominations committee, audit and remuneration committees at the firm.
She is the seventh director to be appointed to the board since Glyn Jones became chairman in September 2016.
Quilter says Ms Markland has “extensive FTSE 100 public company experience” having served over 12 years on the board of Standard Chartered and more than 10 years on the board of The Sage Group.
During her tenure with both companies, she held various positions including senior independent director and chair of the remuneration committee.
She is also a member of the supervisory board of Arcadis NV and an independent non-executive of Deloitte LLP.
Glyn Jones, chairman of the board, said: “I am delighted that Ruth has agreed to join the board.
“Ruth’s extensive skills and experience will be a valuable addition to the board and, as the senior independent director, will provide a wise sounding board to me and my fellow directors.
“Her public company experience will be invaluable as we move into a listed environment.”
• Old Mutual, which has been rebranded as Quilter, announced yesterday that the indicative price range for its float later this month has been set at between 125p to 155p per share.