Central, which recently appointed former Scottish rugby captain Andy Nicol as a corporate ambassador, employs 130 in Scotland and has been on the growth trail since managing director Mr Henry led a management buy-out six years ago.
Marsh, part of New York-based Marsh & McLennan, whose empire includes pensions consultant Mercer, doubles its Scottish presence with the deal and will dominate the broking market. Mr Henry will head its Scottish operations.
Marsh said: "The transaction, which is anticipated to close later in the first quarter of 2014, cements Marsh's already strong leadership position in Scotland and enhances its ability to service corporate clients across a range of industry sectors as well as high net worth individuals."
The value was not disclosed but sources suggested it was north of £10m.
Marsh pounced after Central more than trebled its trading profit to £1m in 2012, paying out £1.2m in director dividends, according to its last published accounts.
Mr Henry commented that strong performance had continued despite "tough times" in the broking market, with over-capacity in the industry and a weak economy. "It is good management, we have been looking at all parts of the business and just tidying things up," he said.
He said Central had benefited from its strong position in the oil and gas sector, while a booming Aberdeen had in the past year also boosted its construction-related business.
Joe Grogan, chief executive of Marsh's corporate business in the UK & Ireland, said Central's targeted 10% annual growth in operating income was attractive as was its range of competencies, which were "very complementary, particularly in the oil and gas sector and the SME sector".
Mr Grogan said the clinching attraction was Central's director profile. "They are committed to the firm, in that stage of their career where they want to continue for the foreseeable future."
Mr Henry said the transaction was "good news" for clients, colleagues and Scottish business.
The accounts show Mr Henry received a £512,000 dividend in 2012, up from £184,000 in 2011, with directors Neil Kerr, David Binnie, Steven Thomson and Chris Tosh each picking up £128,000, a rise from the previous year's £46,000.
Dividends of £64,000, up from £12,500, went to Harry Burness and Graeme Yule, who joined when Central paid £2.6m in 2011 for Aberdeen rival Collins, Halden & Burnett.
Mr Grogan said in a competitive industry where rate rises were unlikely, future growth would continue to come from adding scale. "We don't rely on the insurance market in terms of rate increases, our expectation to be honest is that growth will come predominantly through the acquisition of new clients," he said.
Central's previous acquisitions were aimed at diversifying and broadening its client base away from oil and gas, taking it into Cumbria in 2009, Glasgow in 2010 and Edinburgh in 2011, when it became one of the top 10 brokerages in the UK.
Mr Henry entered the industry 25 years ago and joined Central in 1992, rising to deputy managing director at the time of the sale in January 2008 by founder David Thomson, who started the business in 1973. The buy-out came soon after Central had relocated its then 70-strong staff from Aberdeen city centre to a new £3m headquarters at Westhill.
Two months later, Glasgow's Giles Insurance, founded in 1967 by Mike Giles and bought out by his son Chris Giles and a management team for £46m in 2006, was sold to private equity group Charterhouse Capital.
In an ever-consolidating market, the much-expanded Giles Group, now employing 1250 after 35 takeovers, was sold by Charterhouse last September to New York-based Arthur J Gallagher for £233m.
Last June, Central appointed former British Lion Mr Nicol, a business consultant and former RBS private banking executive, as an ambassador for its bespoke personal insurance service, covering high-value cars, property, art and jewellery.