The 80-year-old billionaire spent almost $3 million in support of legalization bills in the states of Washington and Massachusetts, Forbes reported.
The National Organization for the Reform of Marijuana estimates that he spent more than $40 million on the cause since the 1980s.
"Our marijuana laws are outdated, ineffective and stupid," Lewis told Forbes in a 2011 interview. "I don't believe that laws against things that people do regularly, like safe and responsible use of marijuana, make any sense. "
Lewis, who died of natural causes Saturday, began using the drug at age 39, but also used marijuana to combat pain from a partial amputation of his leg when he was 64.
Lewis graduated from Princeton and took over Progressive from his father in 1965.
At the time of his death, his net worth was more than $1.3 billion.