"When you think about equality and freedom and justice, we've got more work to do," he said.
Common, who also had an acting role in the film based on the historic 1965 march, said it was their duty to speak out, given the stage and setting of the Oscars.
"How could you not say anything, especially representing a film like 'Selma'," he said.
Common credited Oyelowo with ensuring "Selma" was made by getting director Ava DuVernay on board and involving Oprah. The singer said he had called up Legend while he was on tour in London inquiring about collaborating.
"That word really inspired me," Legend said of "Glory". "The song should sound triumphant."
>>For the full Oscar download -- including a list of winners, photos of the best and worst dressed stars and more -- check out coverage from our news partner Dayton Daily News.
The Associated Press contributed to this report.