Online investment platform Interactive Investor has more than 400,000 customers and assets under administration of about £55bn.
Abrdn said the acquisition will “significantly enhance” its presence and growth opportunities within a “fast-growing and attractive market”.
Chief executive Stephen Bird said: “This is a unique opportunity and a transformative step in delivering our growth strategy. Interactive Investor is the UK's number one subscription-based investing platform with a powerful reputation as a consumer champion.
“Abrdn's scale, resources, and shared vision will enable Interactive Investor to grow confidently and expand its leadership position in the UK's attractive savings and wealth market.”
As part of the deal, Richard Wilson, chief executive of Interactive Investor, will join Edinburgh-headquartered Abrdn and continue to lead the investment platform, which will operate as a standalone business within Abrdn's “personal vector”.
Completion of the deal is subject to regulatory and shareholder approval.
Wilson said: “This is an exciting new chapter in our history and means that we can focus exclusively on serving those who matter most: our customers.
“We will have access to Abrdn's additional capabilities across research, advice and wealth management services, and we will benefit from being part of one of Europe's largest investment and wealth management firms, with a vision and values closely aligned to our own.
“Our management will remain the same, and the same extraordinary team will continually develop our service and technology.”