Mattioli Woods says the investment is part of a move to develop a digital, self-investment application.
Tiller Group closed its wealth management robo-adviser service Tiller Investments in 2019 and returned money to investors after deciding to concentrate on wealth management fintech for the B2B market.
It was one of a number of robo-advisers to pull out of the market over the past three years.
Tiller now provides a Software as a Service ("SaaS") wealth management platform for wealth managers and other regulated financial services businesses.
The platform will provide a digital investment management app which will be able to onboard new clients and will offer risk profiling, portfolio management and other services.
Mattioli says it will offer the service at a “competitive price” for clients. The launch is planned for later this year.
Mattioli Woods says it will work with Tiller to develop the automated investment management platform to help extend its discretionary investment management services to more clients.
Mattioli will take an initial shareholding of 4% in Tiller with the potential to increase this in the future.
Michael Wright, Mattioli Woods group managing director, said: "We are very excited about our new relationship with Tiller and the opportunity this will provide for both new and existing clients.
“Technological innovation is key to our ambitious growth strategy and through working with Tiller, we demonstrate our commitment to enhancing our digital offering to clients. This platform will enable us to provide great outcomes to a new client demographic and also allows us to further simplify and enhance the process of bringing on board new clients both efficiently and highly securely - appropriate for a Covid and post-Covid environment".
Ian Cadby, chief executive officer, Tiller Group, said: "Mattioli Woods' requirements fit perfectly with our expertise and experience in designing and building leading-edge customer-facing digital solutions. We have a proven capability in this arena and are proud to have Mattioli Woods as both a client and a shareholder."