Bingham McCutchen has secured a merger with Washington DC’s Swidler Berlin in a move that gives the expansionist Boston giant a 200-lawyer practice in the US capital.

The tie-up will see the 140-lawyer Swidler join forces with Bingham’s 53-lawyer local branch in the first quarter of 2006 after the two firms signed a letter of intent earlier this month. The tie-up will create a top 20 US law firm with a turnover of more than $700m.