The move comes in response to the increased number of multinational deals heading Finsbury's way.
Merrill, who assumed the post of US chief executive at Finsbury on 1 June, was head of Edelman's financial comms practice in the US.
‘We're the leading boutique in the UK and Europe,' said Merrill. ‘In today's global business environment, to not have a platform in the US is a significant hole.'
Merrill added that the move was something that WPP and owner Sir Martin Sorrell had wanted to do ‘for some time'. Finsbury was acquired by WPP for £50m in 2001 (PRWeek, 1 June 2001).
After entering New York, Finsbury will come up against UK-based financial agencies with offices there, such as Brunswick and Financial Dynamics.
College Hill recently told PRWeek it expected to open a New York shop in the near future (PRWeek, 19 May).
Merrill's departure from Edelman follows the exit of three senior New York financial staffers in November.
Deputy general manager Richard Mahony, executive vice-president Bill McBride and senior V-P Doug Donsky all joined Gavin Anderson as managing directors.
Edelman has yet to name Merrill's replacement.