Laura Carstensen is currently non-executive chairman of Park Group and a non-executive director of The Co-operative Bank, where she chairs the values and ethics committee and is a member of the remuneration and risk committees.
Previously she spent 20 years at law firm Slaughter and May where she was a partner and board member.
She has also been deputy chairman of the Competition Commission and a commissioner of the Equality and Human Rights Commission.
The company previously announced that Eamonn Flanagan had also been appointed to its board as non-executive director.
Les Platts, chairman of AJ Bell, said: “Laura adds significant experience to our board which I believe will be invaluable as we prepare for an IPO and beyond.
“We operate in a fast growing sector of the financial services market and our continual focus on the needs of our customers is resulting in controlled and sustained expansion.
“Laura therefore joins us at a very exciting time and will help us continue this momentum through the next phase of our growth and development.”
Laura Carstensen said: “AJ Bell is a fantastic business with values that I greatly admire.
“It has an unwavering focus on helping its customers to invest and the market for those investment services is growing rapidly.
“I am looking forward to working with Les and the rest of the AJ Bell board to help steer the company through the planned IPO, whilst maintaining the commitment to customer service that has served it so well for many years.”