Hammonds has ousted DLA Piper Rudnick Gray Cary from its role as supermarket giant Tesco's main employment law adviser.
The firm's Leeds employment head Mark Shrives led a national team bidding for the work against DLA Piper and a number of other firms.
As first reported on www.thelawyer.com (12 July), Shrives described the appointment as "extremely exciting", adding: "We were giving advice that's about solving their problems, not about being lawyers."
The win will see Hammonds advise Tesco on all of its tribunal work and give employment advice to the company's stores, headquarters and distribution centre, as well as providing HR advice. The appointment is for an initial period of one year, but is expected to last longer.
DLA Piper has been Tesco's employment adviser for a number of years, with Birmingham employment partner Peter Thompson leading the relationship. Thompson was unavailable for comment.
A DLA Piper spokesperson said: "We've retained our role as adviser to the group HR director to support Tesco internationally."