Parker said that the EU had helped solve "incredibly complicated old problems and if they can find a way to be a community ... that is an ideal. It is what I want for us."
Butler, who worked as a lawyer before becoming an actor, said he lived much of his early life in Scotland, "which has had a very tragic history fighting against England for thousands of years."
"Now we live in a time when this isn't happening, and I think as a Scotsman, as a European, it makes me very proud to be part of this process," he said.
The evening's artists, performing at Oslo's Spektrum Hall, include U.S. singer Jennifer Hudson, Australian pop star Kylie Minogue, American R&B artist Ne-Yo, and British soul singer Seal.