Mr Manduca will join the SJP board as a non-executive director and chair designate on 1 January.
Iain Cornish joined the SJP board in 2011 and became chair in 2018. He will step down as a director at the 2021 AGM.
Mr Manduca has been chairman of Prudential since July 2012. He joined the board as senior independent director in October 2010 and is due to step down from Prudential on 31 December.
He has a long track record of senior roles in financial services. He was the founding CEO of Threadneedle Asset Management, global CEO of Rothschild Asset Management and European CEO of Deutsche Asset Management.
He has also been senior independent director of Morrison Supermarkets and a non-executive director of KazMunaiGas Exploration & Production. He is currently chairman of Templeton Emerging Markets Investment Trust.
Mr Manduca said: "I am honoured to be asked to join the board and to become chair of St James's Place.
“I have long admired St James's Place for the unique service it offers to its clients of expert financial advice and a distinctive approach to investment management. I look forward to working with the whole SJP community as St James's Place continues its development as the leading provider of long-term Financial Planning at a time when the need for this is greater than ever."
Roger Yates, senior independent director of St James's Place plc, said: "'I am delighted that our thorough search process has resulted in the selection of Paul Manduca as our next chair. He has extensive boardroom experience across the financial services sector and his expertise will be invaluable to St. James's Place.
“The board and I would like to thank Iain for his service to St James's Place as chair and as a director since 2011. We have benefited immensely from his wise counsel and guidance during that period."
Iain Cornish, chair of St James's Place plc, said: " It has been a huge privilege to chair the board at St James's Place. I will leave behind a strong board and management team running a successful company with a great future. I welcome Paul to St James's Place and wish Paul, the board and SJP every success in the future."