Partners at Thelen Reid & Priest and New York’s Brown Raysman Millstein Felder & Steiner voted to combine the two firms Monday, creating a 617-lawyer firm that, based on last year’s revenue, would have placed 56th on the Am Law 100 list.

The firm will be called Thelen Reid Brown Raysman & Steiner, and will be co-chaired, for 2 1/2 years, by Stephen O’Neal, Thelen’s chairman, and Julian Millstein, Brown’s co-managing partner.