John Gregg (1957? - February 1, 2003) was a senior member of the UDA/UFF Loyalist organization in Northern Ireland.

On March 14, 1984, he severely wounded Sinn Féin president Gerry Adams in an assassination attempt for which he was jailed.

Gregg was part of the group of senior UDA figures that expelled Johnny Adair from the UDA in September 2002. He was killed along with another UDA member, while travelling in a taxi. The murder was blamed on supporters of Johnny Adair, who was himself by then in prison. Days later, family and supporters of Adair fled to Scotland after death threats.