They will advise primarily on commercial, regeneration and major projects work, including a Newcastle waste management project.
Head of commercial at Newcastle City Council John Softly said: “[The joint panel is intended] to provide expertise and capacity where we don’t have it in-house.
“The main reason was to achieve value for money in terms of our external spend through discounted rates from these providers.”
The member councils are Newcastle, Gateshead, North Tyneside, South Tyneside and Sunderland.
The five councils have a joint in-house capability of around 120 lawyers.