The PM was given the honour at the plant in Cowley where the new-look Minis have been manufactured since 2001.
Of the two million, more than 1.5 million Mini’s have been exported to customers in more than 90 countries around the world from Australia to Venezuela.
Mr Cameron congratulated Mini staff and said he was “very proud” to be there to mark the achievement.
The PM said:
It’s a remarkable story, to take that iconic British brand, to give it this great modernisation and then to produce version after version. It has had enormous success all over the world. It is a fantastic success story.
The export success of the Mini and BMW’s continued investment in its UK operations have helped contribute to a “real renaissance” for the UK car industry, the PM said.
MINI is not just a symbol of our industrial past, but also the great industrial future we want to build.”
In June, Mr Cameron welcomed members of the European automobile manufacturers association to Downing Street where he said the Government was determined to do everything to help the automotive industry succeed in the UK.