The venue in Chiswell Street, London is now part of the private property fund St James Capital (SJC), headed up by EC&O chief executive Anthony Lyons.
He said: "This move is part of a wider strategy to focus on acquisitions which we believe have a significant role to play in the future direction and growth of Earls Court and Olympia."
SJC will invest in developing the EC1 venue's facilities and infrastructure over the next 18 months.
The Brewery, which was placed on the market in July, employs around 100 people, who have now transferred to the EC&O group.
EC&O director of communications Rebecca Salt said: "We're looking to expand our current conference and exhibition facilities and the Brewery provides us with capacity for 900 delegates, which fits in with our aim to grow a leading exhibition and conference venue portfolio in central London
"The first three months we will be finding our way around a business with a good reputation, and it's the people that make that reputation."
The Brewery, built in 1782, offers nine rooms and features a vaulted timber roof in its largest space, the 778sqm Porter Tun room. The venue reported a turnover of £8.7m for the year ending February 2005.
The chief operating officer of SJC and EC&O, Simon Conway, worked with Investec Bank's property finance team Derrick Beare and Daniel Austin during the acquisition. Property and leisure agent Davis Coffer Lyons advised the purchasers.
EC&O stages more than 170 shows a year, attracting 3.8m visitors and 25,000 exhibitors.