One of Boston’s best-known independent real estate firms is going national.

Otis & Ahearn has reached a deal to be acquired by Douglas Elliman, a New York company that’s one of the country’s largest luxury real estate brokerages.

Otis & Ahearn’s Boston offices will remain in place, but the deal will enable it to tap into the global relationships and marketing of a national firm to sell high-end Boston real estate around the world, said Kevin Ahearn, Otis & Ahearn’s president, who founded the company in 1978. The selling price was not disclosed.

“Boston’s in a different place in the world now,’’ Ahearn said. “In the past, we didn’t have this global market, global economy. We need scale and a platform, and [Douglas Elliman] has thrived in that space.’’

Ahearn said he spent two years looking for the right company to partner with to help tap growing demand for high-end Boston housing. Douglas Elliman, which has 113 offices across the United States and a partnership with global real estate firm Knight Frank, was his first choice, he said.

For Douglas Elliman, a Boston presence makes sense, chairman Howard M. Lorber said. His firm does a lot of business in New York, the Hamptons on Long Island, Aspen, Colo., and South Florida, markets with strong connections here.

And, he said, the wave of luxury condo development will give Douglas Elliman the chance to market new buildings.

“We thought it was a natural, and we wanted to wait for the right opportunity,’’ Lorber said. “We try to enter markets where we think we can make a real dent in new development.’’

The deal is expected to close in October. No financial details were shared, but Ahearn will stay on as chief executive of the firm’s Boston division.

Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.