The CEO of major US insurer Progressive has proven his liberal bona fides with a major donation to a campaign to legalise cannabis in California.

The $US209,005 ($210,969) donation by Peter Lewis in support of Proposition 19 – known as the Regulate, Control and Tax Cannabis Act of 2010 – is the latest contribution from the billionaire insurance magnate following a $US3 million ($3.02 million) donation to the Marijuana Policy Project in 2007.

Californians vote on the ballot proposition on November 2. It would legalise various marijuana-related activities and allow local government to regulate and collect related fees and taxes.

For Mr Lewis, legalisation of the drug is deeply personal. After having part of his left leg amputated in 1998, he smokes the drug as prescribed by a doctor for pain relief.

His public role in cannabis legalisation began after he was fined by a New Zealand court for possession.