Ezickson, who is co-head of the international energy practice, takes over as London office head from David Dalgarno.
Dalgarno said he was "delighted" to be standing down and returning to practice in the employment group.
He said the London office would continue to grow, adding: "The various departures have distracted from the fundamentals. The underlying business is very strong and it is getting stronger."
After leading the UK team for four years, Dalgarno will take up a position on the firm's five-member compensation committee.
Ezickson will also become the head of McDermott's European practice when his tenure begins at the end of March. He said he would focus on cross-border collaboration and expanding the European network, adding: "There is no doubt that London will be a key driver in helping us to deliver our growth strategy, and I am excited by the prospect of leading this effort."
Ezickson has been at McDermott for 14 years and was head of the Boston office before moving to London two years ago.
He has served on the firm's management committee for seven years, the executive committee for three years and spent several years as head of business development and marketing.
McDermott has set its sights on aggressive expansion of its London office in 2008, a year in which the firm celebates its 10 anniversary in the city. In January it lured corporate star Hugh Nineham from Lovells to lead the corporate practice.