Lord Leitch is to step down from his role of chairman of adviser network Intrinsic Financial Services at the end of March, prompting a shake-up of the firm's board.
The Labour peer and former deputy chairman at Lloyds Banking Group will also leave his position as non-executive director of Old Mutual Wealth as part of the move.
He will be replaced at Intrinsic by current independent non-executive director Gregor Stewart, who will take over as chairman in April, while Lord Leitch will stay on as an adviser to the board until June.
Intrinsic CEO Andy Thompson said: "[Lord Leitch's] contribution to Intrinsic, as well as Old Mutual Wealth, has been immense.
"As a founding shareholder, director and chairman of Intrinsic, he has been pivotal to the success of our business through its start-up phase and was instrumental in the acquisition of the business by Old Mutual Wealth in July 2014."
The venture, run by former Sanlam UK distribution director Nigel Speirs, acts as an appointed representative of Intrinsic and is aimed at "underserved segments" of the market.
Parent company Old Mutual meanwhile has entered what it called a "managed separation"
of its four core businesses - Old Mutual Emerging Markets, Old Mutual Wealth, Nedbank Group and OM Asset Management in the US.
It has plans to de-merge from Old Mutual Wealth, which will subsequently be listed on the London stock exchange.