The Financial Conduct Authority has approved AssetCo's £4.1m purchase of Ocean Dial Asset Management.
Although still waiting on Indian regulatory approval, AssetCo said the requisite clearances were "at an advanced stage".
The offer, which was made in March of this year, will see the Martin Gilbert-chaired asset manager incorporate emerging markets within the firm for the first time.
The purchase will be made with £2.1m in cash and the issue of 2,928,258 ordinary shares of £0.01 each
AssetCo said Ocean Dial's India Capital Growth Fund investment trust, which currently holds £150m in assets under management, will be brought under the River and Mercantile banner.
With the deal receiving FCA approval on Indian Independence Day (15 August), Gilbert said: "The approval of the FCA is a significant step forwards and brings us closer to completing our acquisition of Ocean Dial, which will broaden and strengthen our equity management capability.
"India is making significant progress and its economy has the potential to match or even overtake those of the US and China in the longer term.
"The country is home to some market leading companies and a remarkable pool of talent. We are excited to be one step closer to being able to complete our acquisition of Ocean Dial."
Gaurav Narain, co-head of equities at Ocean Dial, noted that India now has more than twice the number of quoted companies as the UK, totalling over 5000 in India compared to 1925 in the UK.
"The India stock market is responding. The valuation gap is closing," he added.
"The market is not differentiating between large and mid-cap companies. Valuations instead are a function of quality of business; quality of management, sustainable growth and cash generation and returns."
