Sandwell will join Walsall, Birmingham, Coventry, Dudley, Solihull and Wolverhampton councils to make up the Combined Authority, which hopes of securing additional powers from Whitehall.
Council leader Darren Cooper said: “This decision is a big step towards creating a combined authority for the West Midlands.
“The fact it was a unanimous decision shows a real appetite for us to join forces and work with our fellow councils. This will allow us to secure the best economic outcomes and make sure we have more of a say for our region.”