Brendan Eich received his bachelor's degree in math and computer science at Santa Clara University. He received his master's degree in 1986 from theUniversity of Illinois at Urbana-Champaign.

Eich started his career at Silicon Graphics, working for seven years on operating system and network code. He then worked for three years at MicroUnity Systems Engineering writing microkernel and DSP code, and doing the first MIPS R4000 port of gcc.

Eich is best known for his work on Netscape and Mozilla. He started work at Netscape Communications Corporation in April 1995, working on JavaScript(originally called Mocha, then called LiveScript) for the Netscape Navigator web browser. In 2010, he wrote about JavaScript: "JS had to "look like Java” only less so, be Java’s dumb kid brother or boy-hostage sidekick. Plus, I had to be done in ten days or something worse than JS would have happened".

He then helped found mozilla.org in early 1998, serving as chief architect. When AOL shut down the Netscape browser unit in July 2003, Eich helped spin out the Mozilla Foundation.

In August 2005, after serving as Lead Technologist and as a member of the Board of Directors of the Mozilla Foundation, Eich became CTO of the newly founded Mozilla Corporation.