Massachusetts Republicans had hoped Brown would run in the special election for the seat left vacant by Kerry's appointment as secretary of state, and some speculated he'd make a bid for governor in 2014, The Hill reported Monday.
Brown's contract with law and lobby firm Nixon Peabody is likely to be long-term, though, the newspaper said.
The firm said Brown will concentrate his practice on "business and governmental affairs as they relate to the financial services industry, as well as on commercial real estate matters."
"During my time in politics, I never hesitated to reach across the aisle to work with members of any political party to secure a preferable outcome. My approach is consistent with the way Nixon Peabody does business and I believe we can be successful together," Brown said in a statement.
The former senator has also committed to Fox News as a commentator, The Hill reported.