The deal worth over $300m was first agreed in February 2011 and was referred by the Office of Fair Trading to the Competition Commission in June 2011.
BATS is planning to combine Chi-X Europe with the BATS Europe multilateral trading facility.
The new company, to be known as BATS Chi-X Europe, will take about a quarter of all European equities trading.
In the third quarter of 2011, Chi-X Europe traded EUR546.6bn worth of shares and took 19.5% of the overall European market share and BATS Europe reached EUR154.2bn and took a 5.5% market share.
BATS Global Markets chairman and CEO Joe Ratterman said that they will now focus on completing the combination of BATS Europe and Chi-X Europe to create an even more formidable competitor in pan-European securities trading, offering greater market efficiencies for the entire investing community.
