The board is intended to give a voice to social groups who may face discrimination or disadvantage, and bring together representatives from the social economy, faith and community groups, businesses, trades unions and young people.
Rotheram said: “In my manifesto I pledged to put fairness and social justice centre stage.
"Bringing in someone with Lynn’s credibility and track record of fighting poverty and its causes demonstrates my determination to deliver on this pledge."
He added: "I am delighted that Lynn has agreed to take on this role to be our ‘critical friend’, as we get to work on increasing prosperity in a way that must benefit all across the city region.”
The board would provide independent advice to the combined authority and be “permanently holding our feet to the fire on a core commitment”, Rotheram stated.
Rotheram said similar formal commitments to fairness had helped increase prosperity in other cities including Portland, Seattle, Zurich and Copenhagen.
