He co-founded Sun Microsystems in 1982 along with Scott McNealy, Vinod Khosla, and Andy Bechtolsheim, and served as Chief Scientist and CTO at the company until 2003.

He played an integral role in the early development of BSD UNIX while being a graduate student at Berkeley,[1] and he is the original author of the vi text editor.

[5] A few of his other accomplishments have also been sometimes exaggerated; Eric Schmidt, CEO of Novell at the time, inaccurately reported during an interview in PBS's documentary Nerds 2.0.1 that Joy had personally rewritten the BSD kernel in a weekend.

[9] According to a Salon article, during the early 1980s, DARPA had contracted the company Bolt, Beranek and Newman (BBN) to add TCP/IP to Berkeley UNIX.

[15] On September 9, 2003, Sun announced Joy was leaving the company and that he "is taking time to consider his next move and has no definite plans".

[22] In 2011, he was inducted as a Fellow of the Computer History Museum for his work on the Berkeley Software Distribution (BSD) Unix system and the co-founding of Sun Microsystems.

[23] In 2000, Joy gained notoriety with the publication of his article in Wired magazine, "Why The Future Doesn't Need Us", in which he declared, in what some have described as a "neo-Luddite" position,[24] that he was convinced that growing advances in genetic engineering and nanotechnology would bring risks to humanity.

After bringing the subject up with a few more acquaintances, he states that he was further alarmed by what he felt was that although many people considered these futures possible or probable, that very few of them shared as serious a concern for the dangers as he seemed to.

[27] He has also raised a specialty venture fund to address the dangers of pandemic diseases, such as the H5N1 avian influenza and biological weapons.