Silicon Valley leader Cooley Godward is to finally enter New York after securing a tie-up with litigation boutique Kronish Lieb Weiner & Hellman – a move hailed as one of most significant US mergers of recent years.

The tie-up, which goes live on 1 October under the banner Cooley Godward Kronish, will create a 550-lawyer national practice and comes after several years in which Cooley had sized up mergers with a handful of very different firms.