After graduation from Caltech, he went to work in the computer gaming field for a company that developed video games such as Adventures of Tron, Armor Ambush, Astrosmash and Space Attack. He later went to work for the PGP Corporation with whom he remained until his retirement in 2011.
Finney was a noted cryptographic activist. During the early 1990s, in addition to being a regular poster on the cypherpunks listserv, Finney ran two anonymous remailers. Further cryptographic activism included running a (successful) contest to break the export-grade encryption Netscape used.
In 2004, Finney created the first reusable proof of work system before Bitcoin. In January 2009, Finney was the Bitcoin network's first transaction recipient.