The parties are now in opposition together at Stormont.
Since going into opposition after the assembly election in May, the effectiveness of the arrangement between the Ulster Unionists and the SDLP has been constantly questioned.
The decision to invite Colum Eatwood to address the UUP conference can be seen as the response to that criticism.
Ulster Unionist leader Mike Nesbitt said there was a lot of joined up work going on between the parties but he and Mr Eastwood were conscious people want to see tangible signs of co-operation.
Rather than dwell on what divides them, he said, they were focused on common ground, importantly the fact both want Northern Ireland to work.
Mr Eastwood said it was a demonstration of what genuine co-operation looks like - two leaders of parties with different views coming together in the interests of people who deserved better from the current Executive.
"It's the principle of partnership, ingrained in our institutions by the SDLP and UUP and degraded by the current government, that brings us together on issues of common cause where we can make a positive difference to the lives of the people we represent," he said.
Mr Nesbitt said that while there was a lot of co-operation between the UUP and SDLP behind the scenes, he was conscious that people wanted to see tangible signs of it.
"We will not agree on everything, but rather than dwell on what divides us, I am focused on the common ground, and importantly, the fact that Colum and I both want Northern Ireland to work, which opens huge possibilities for cooperating on the bread and butter issues of the economy, education, housing and the health of all our people," he said.
An SDLP leader will speak at the Ulster Unionist conference for the first time on Saturday.