Lacob grew up in a Jewish family in New Bedford, Massachusetts. His father worked at a paper products company, his mother at a local supermarket. His favorite team in boyhood was the Boston Celtics of the NBA. When he was 14, the company that employed his father was sold. The only worker the new owners retained was his dad. The Lacob family relocated to Anaheim, California and Joe switched his allegiance to the Los Angeles Lakers and the Los Angeles Angels of Anaheim.
Lacob earned a bachelor's degree in biological sciences from the University of California, Irvine (UCI), a master's in public health (epidemiology) from University of California, Los Angeles (UCLA) and an MBA from the Stanford Graduate School of Business.  "I was a very poor kid," Lacob recalled. "Had nothing. I paid every dime of my education through college. Every single dime. I was the first person to graduate from college in the history of my family. Ever. I came from nothing."
Lacob has been a partner at Kleiner Perkins, a Venture capital investing firm, since 1987. His investments have centered around firms involved in life sciences, medical technology, Internet and energy, and such enterprises as AutoTrader.com, Invisalign and NuVasive. Before he joined Kleiner Perkins, Lacob held executive positions with Cetus Corporation (now Chiron), FHP International (a health maintenance organization) and the management-consulting firm of Booz, Allen & Hamilton. In interviews, he has credited his epidemiology degree for giving him a background in statistics that has fed the statistical side of his longstanding sports interest.
He was a primary investor in the American Basketball League, a professional women's basketball league that eventually folded from failure to compete successfully with its rival, the Women's National Basketball Association (WNBA). In January 2006 he became part-owner of the Celtics, where he became a co-investor with H. Irving Grousbeck, an entrepreneur and a professor at the Stanford Graduate School of Business. On July 15, 2010, Lacob and the group of investors he headed agreed to buy the Golden State Warriors of the NBA from Chris Cohan for $450 million, requiring him to sell his minority interest in the Celtics. The Lacob - Peter Guber group won out over a dozen other bidders for the Warriors, including Oracle chief executive officer Larry Ellison, 24-Hour Fitness founder Mark Mastrov and Texas billionaire financier David Bonderman. He had been a Warriors' season-ticket-holder for about a decade. He already had extensive experience operating an NBA team as part-owner of the Boston Celtics, and also points to his friendships with two major league baseball team general managers, Billy Beane of the Oakland Athletics and Jeff Moorad of the San Diego Padres, who have both proven that winning records are not solely related to the size of the team payroll. Lacob approved the acquisitions of David Lee and undrafted rookie guard Jeremy Lin, a hometown favorite. He also fired coach Don Nelson and replaced him with assistant coach Keith Smart. The sale was unanimously approved by the NBA league's board of governors on November 12, 2010. Lacob and Peter Guber are the chief owners, but Lacob is in charge of day-to-day operations.
Before the 2014-15 NBA season Lacob fired coach Mark Jackson who had just led to the Warriors to the playoffs in back-to-back seasons. Lacob explained the decision at a conference of fellow venture capitalists: "Part of it was, he couldn't get along with anybody else in the organization. And, look, he did a great job -- and I'll always compliment him in many respects -- but you can't have 200 other people in the organization not like you." 
- Ross, Andrew (July 16, 2010). "New owner Lacob is passionate about Warriors". San Francisco Chronicle.
- Howard-Cooper, Scott (October 19, 2010). "Warriors hope Lee, new philosophy mean return to playoffs". NBA.com.
- ESPN Grantland: "The Winter of Jerry West - Catching up with The Logo at his home in West Virginia" By Jonathan Abrams October 5, 2011
- Thompson II, Marcus (March 11, 2011). "Lacob's dream comes true -- partially". San Jose Mercury News. Archived from the original on March 11, 2011.
- Smith, Marcia C. (June 12, 2008). "Orange County boy returns to area as part owner of Celtics". Retrieved March 11, 2008.
- Kleiner Perkins website
- Proxy statement for Align Technology, as quoted at Forbes.com
- see Kawakami interview, part 3
- Boston Celtics press release January 18, 2006
- NBA press release July 15, 2010, "Report: Warriors sold for record $450 million"
- Thompson II, Marcus (2010-11-13). "Group headed by Joseph Lacob, Peter Guber finally gets NBA approval to take over Golden State Warriors". The San Jose Mercury. Archived from the original on 2010-11-14. Retrieved 2010-11-14.
Even before the NBA approved the sale, Lacob had a hand in personnel decisions with Cohan's blessing.
- see Kawakami interview, part 2
- Simmons, Rusty (February 4, 2011). "Nelson cites Warriors' effort, calls roster flawed". San Francisco Chronicle. Archived from the original on February 6, 2011.
It was done really professionally," Nelson said. "I talked to (Lacob) on the phone before I got fired, and I was really impressed. I was a little surprised with the way things happened, but I think it is for the best for everybody.