Corporate lawyer, Karasz - who joined the firm in 1967 - replaces Ned Stiles who held the post for 12 years.
Karasz ran the firm's Paris office for five years and more recently has been concentrating on transnational joint venture schemes in the US, Latin America and Europe.
He has worked extensively on cross-border transactions which fits in wellwith Cleary Gottlieb's international bent: about a third of the firm's 600 lawyers working outside the US.
He says he wants to carry on developing the firm's international strategy, focusing particularly in its M&A and capital markets practices. London firms hoping to lure Cleary Gottlieb into a transatlantic merger are out of luck though. At least for the moment.
Karasz says it is "hard to say never" but adds that the firm's lengthy European presence and US strengths, made such a move unlikely.
"We don't anticipate merging with any other firm because we don't know any other firm that would suit us," he adds.