The chief executive of the new trading company formed by the merger of Getco and Knight Capital Group said he expects global securities-market activity to ramp up when the US Federal Reserve trims efforts to stimulate the economy.

The two firms on Monday completed their merger into a new company called KCG Holdings that its executives estimate is the largest market-making firm in the US stock market. In an interview, KCG CEO Daniel Coleman said the Fed's move to scale back its quantitative easing programs, when it comes, will remove a big hurdle facing the new company.