The Swindon plant began production of the Civic on September 19, 1994, and in its first year 6,652 were built there. This year, the £1.38bn factory will produce 136,792 Civics.
The millionth Civic, a red UK-spec Type R, rolled off the production line on Friday.
David Hodgetts, HUM director, said: “We are the only Honda plant in the world manufacturing the Civic 5-door and 3-door models and are extremely proud of the fact there are one million happy customers driving Swindon-built Civics.”
Over the past 12 months, HUM has increased production from 190,000 to 250,000 units due to increasing demand for the three and five door Civic models and the latest CR-V, all of which are built at Swindon.
The factory now employs 5,000 people.