Morrissey, who spent just 14 months on SJP’s board, will succeed Les Platts as AJ Bell's chairman at the company's next annual general meeting, which is expected to take place in January 2022.
In the meantime she will join the board as chair designate in July.
Platts said: “It has been a great honour to chair the board at AJ Bell and to help steer the company through its successful IPO in 2018.
"The business is full of great people who are totally focused on serving its customers and I’ll leave knowing it has a very bright future.”
Morrissey, a Conservative peer who is also lead non-executive director for the Foreign, Commonwealth and Development Office, was previously head of personal investing at Legal & General Investment Management.
Before this she was chief executive of Newton Investment Management.
In her role as an SJP director, Morrissey made headlines when she described the company's fee structure as untransparent, saying she was unable to “explain them very quickly”.
Commenting on her appointment, Morrissey said: “I’ve long admired AJ Bell and its commitment to helping people to invest. Its low-cost, easy to use investment platform is exactly what people need to help them start their investing journey and build financial security for themselves and their families.
“The business is growing quickly and I’m looking forward to joining the team to help build on that success and shape the future direction of the company.”
Beyond her corporate roles, Morrissey was also the founder of the 30% Club - which campaigns for greater female representation on company boards.
Also joining to AJ Bell board as a non-executive director is Evelyn Bourke, who currently sits on the Marks & Spencer board.
She was chief executive of Bupa until December 2020 and previously held senior roles at a number of financial services businesses including Friends Provident, Standard Life and Chase de Vere.
Bourke commented: “AJ Bell is a fantastic business operating in an exciting part of the market. More than ever people need to take control of their long-term savings and investments, whether that be via a financial adviser or doing it themselves.
“Whichever route they prefer, AJ Bell offers the products and investment solutions they need to build and manage their wealth and I’m looking forward to contributing to the next phase of its development.”
Laura Carstensen, senior independent director at AJ Bell, added: “The appointments of Helena Morrissey and Evelyn Bourke further strengthen the AJ Bell board and will help develop the company’s ambitious growth strategy.
“They each have a broad depth of experience in a range of financial services business and we are confident this will bring new ideas to the business that will benefit all our stakeholders.
"The board and I would like to thank Les for the vital role he has played in the growth and success of AJ Bell as a director since 2008 and as chair since 2014.”
