The phrase "prominent campaigner" refers to someone who is well-known and actively advocates for a specific cause or idea. They are visible and influential in promoting and raising awareness about the issue they care deeply about. Full definition
In fact, contributors Bob Cummings, Irving Stowe and Paul Watson — who went on to found the Sea Shepherd Conservation Society — were among the founders and prominent campaigners for Greenpeace. (straight.com)
Chris Huhne, the Lib Dem energy secretary and prominent campaigner for a yes vote, accepted that there would be no further attempt to introduce voting reform during this parliament and that it was «over» for AV. (theguardian.com)
«I'm so happy,» said his beaming wife, Lilian Tintori, who has become a prominent campaigner for the opposition. (businessinsider.com)