Walsh will advise clients about working with all levels of government, drawing on his experience as chairman of several House Appropriations subcommittees during his 10-term career in Congress.
Walsh, 61, will be banned under congressional ethics rules from lobbying any member of the House or Senate, or their staffs, for one year after leaving office.
Walsh said he has no plans to return to politics.
K&L Gates LLP is a US law firm with over 1700 attorneys worldwide and is ranked as the 10th largest law firm in the world.