Murphy, a former minister under Tony Blair and Gordon Brown, founded Arden Strategies shortly after losing his parliamentary seat in 2015.
It has lobbied Sir Keir’s administration on behalf of arms manufacturers, oil companies and energy giants, according to the public register of consultant lobbyists.
The company is not listed as a member of trade body Public Relations and Communications Association (PRCA), which requires members to list all their public affairs clients.
Arden provided support to more than 30 prospective Labour MPs in the run-up to the 2024 general election, according to social media posts seen by the BBC.
The total amount Arden spent is not known because the individual sums appear to have fallen below the threshold for sponsorship to be declared by MPs.
Labour Party chair Anna Turley and business minister Blair McDougall used to work for the lobbying firm. Former Labour MP Holly Lynch is listed as a current employee.
There is no suggestion Turley, McDougall or Lynch were involved in any events offering access to government employees.
Murphy was a Labour MP for 18 years and held ministerial jobs in the New Labour years, including as Europe minister and Scottish secretary.
He was shadow defence secretary and shadow international development secretary under Ed Miliband’s leadership before briefly leading Scottish Labour and then losing his East Renfrewshire seat at the 2015 general election.