James Hay has struck a deal with Towry for around 4,000 Towry Sipp clients to be transferred into the flagship James Hay Modular iPlan.
The agreement also means that James Hay will become a "key partner in the provision of retirement solutions", the companies announced.
In a statement, the firms said: "A dedicated James Hay transition team will manage the transfer, with completion due in the second half of this year.
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"Once transferred across, Towry's advisers will benefit from the platform's sophisticated online management portal, online trading capability, performance reporting and a range of interactive drawdown tools.
"As part of the platform's ongoing drive to automate processes, valuations and annual reviews will be provided digitally with capability for all instructions to be done online."
James Hay chief executive Alastair Conway said: "The direction we've taken in evolving and growing our business matches perfectly the new and dynamic retirement wealth planning opportunities - that shows in our flows and in the calibre of our strategic partners."
Towry head of client proposition John Porteous said: "We are always looking to deliver the very best service to our clients.
"With such exciting changes in the retirement space, this new arrangement will allow us to focus on our expert retirement planning advice and management of client investments."