Steve Wozniak was born in San Jose, California, the son of Francis Jacob "Jerry" Wozniak (1925–1994) from Michigan and Margaret Louise Wozniak (née Kern) (1923–2014) from Washington State. He graduated from Homestead High School in 1968.

In 1969, Wozniak returned to the Bay Area after being expelled from University of Colorado Boulder in his first year for sending prank messages on the university's computer system. During this time, as a self-taught project, Wozniak designed and built a "Cream Soda" computer with his friend Bill Fernandez. He later re-enrolled at De Anza College and transferred to University of California, Berkeley in 1971. Before focusing his attention on Apple, he was employed at Hewlett-Packard (HP) where he designed calculators. It was during this time that he befriended Steve Jobs.

In the early 1970s, Wozniak was known as "Berkeley Blue" in the phone phreak community, after he made a blue box.

Wozniak was introduced to Jobs by Fernandez, who attended Homestead High School with Jobs in 1971. Jobs and Wozniak became friends when Jobs worked for the summer at HP, where Wozniak too was employed, working on a mainframe computer. This was recounted by Wozniak in a 2007 interview with ABC News, of how and when he first met Jobs:

In 1973, Jobs was working for arcade game company Atari, Inc. in Los Gatos, California. He was assigned to create a circuit board for the arcade video game Breakout. According to Atari co-founder Nolan Bushnell, Atari offered $100 (equivalent to $551 in 2017) for each chip that was eliminated in the machine. Jobs had little knowledge of circuit board design and made a deal with Wozniak to split the fee evenly between them if Wozniak could minimize the number of chips. Wozniak reduced the number of chips by 50, by using RAM for the brick representation. Too complex to be fully comprehended at the time, the fact that this prototype also had no scoring or coin mechanisms meant Woz's prototype could not be used. Jobs was paid the full bonus regardless. Jobs told Wozniak that Atari gave them only $700 and that Wozniak's share was thus $350 (equivalent to $1,929 in 2017). Wozniak did not learn about the actual $5,000 bonus (equivalent to $27,564 in 2017) until ten years later, but said that if Jobs had told him about it and had said he needed the money, Wozniak would have given it to him.

On June 29, 1975 Wozniak tested his first working prototype, displaying a few letters and running sample programs. It was the first time in history that a character displayed on a TV screen was generated by a home computer. With the Apple I design, he and Jobs were largely working to impress other members of the Palo Alto-based Homebrew Computer Club, a local group of electronics hobbyists interested in computing. The Club was one of several key centers which established the home hobbyist era, essentially creating the microcomputer industry over the next few decades. Unlike other Homebrew designs, the Apple had an easy-to-achieve video capability that drew a crowd when it was unveiled.

On April 1, 1976, Jobs and Wozniak formed Apple Computer (now called Apple Inc.) along with administrative supervisor Ronald Wayne, whose participation in the new venture was short lived. Wozniak resigned from his job at Hewlett-Packard and became the vice President in charge of research and development at Apple. He and Jobs decided on the name "Apple" shortly after Jobs returned from an apple orchard in Oregon. Wozniak's Apple I was similar to the Altair 8800, the first commercially available microcomputer, except the Apple I had no provision for internal expansion cards. With expansion cards the Altair could attach to a computer terminal and be programmed in BASIC. In contrast, the Apple I was a hobbyist machine. Wozniak's design included a $25 microprocessor (MOS 6502) on a single circuit board with 256 bytes of ROM, 4K or 8K bytes of RAM, and a 40-character by 24-row display controller. Apple's first computer lacked a case, power supply, keyboard, and display, all components the user had to provide.

He is a Freemason, despite not having faith in a supreme being (which is required by Masonic rules except in "Liberal" or Continental Freemasonry). Wozniak describes his impetus for joining the Freemasons as being able to spend more time with his then-wife, Alice Robertson, who belonged to the Order of the Eastern Star, associated with the Masons. Wozniak has said that he quickly rose to a third degree Freemason because, whatever he does, he tries to do well. He was initiated in 1979 at Charity Lodge No. 362 in Campbell, California, now part of Mt. Moriah Lodge No. 292 in Los Gatos.

In the mid-1980s he designed the Apple Desktop Bus, a proprietary bit-serial peripheral bus introduced on many later Macintosh and NeXT computer Models. However, even with the success he helped create at Apple, Wozniak felt that the company was hindering him from being who he wanted to be, and that it was "the bane of his existence". He enjoyed engineering, not management, and said that he missed "the fun of the early days". Although its products provided about 85% of Apple's sales in early 1985, the company's January 1985 annual meeting did not mention the Apple II division or employees, a move that frustrated Wozniak. As other Engineers joined the growing company, he no longer felt needed there and by early 1985, Wozniak left Apple again, stating that the company had "been going in the wrong direction for the last five years". He then sold most of his stock.

Wozniak was married to slalom canoe gold-medalist Candice Clark from June 1981 to 1987. They have three children together, the youngest being born after their divorce was finalized. After a high-profile relationship with Actress Kathy Griffin, who described him on Tom Green's House Tonight in 2008 as "the biggest techno-nerd in the Universe", Wozniak married Janet Hill, his current spouse.

In May 1982 and 1983, Wozniak, with help from professional concert promotor Bill Graham, founded and sponsored two US Festivals to celebrate evolving technologies; they ended up as a Technology exposition and a rock festival as a combination of music, computers, television and people. After losing several million dollars on the 1982 festival, he stated that unless the 1983 event turned a profit, he would end his involvement with rock festivals and get back to designing computers. Later that year, Wozniak returned to Apple product development, desiring no more of a role than that of an Engineer and a motivational factor for the Apple workforce.

Despite leaving Apple as a day-to-day employee in 1985, Wozniak chose to never remove himself from the official employee list, and continues to represent the company at events or in interviews. Today he receives a stipend from Apple for this role, estimated to be $120,000 per year. He is also an Apple shareholder. He maintained a friendly acquaintance with Steve Jobs until Jobs' death in October 2011. However, in 2006, Wozniak stated that he and Jobs were not as close as they used to be. In a 2013 interview, Wozniak said that the original Macintosh "failed" under Steve Jobs, and that it was not until Jobs left that it became a success. He called the Apple Lisa group the team that had kicked Jobs out, and that Jobs liked to call the Lisa group "idiots for making [the Lisa computer] too expensive". To compete with the Lisa, Jobs and his new team produced a cheaper computer, one that, according to Wozniak, was "weak", "lousy" and "still at a fairly high price". "He made it by cutting the RAM down, by forcing you to swap disks here and there", says Wozniak. He attributed the eventual success of the Macintosh to people like John Sculley "who worked to build a Macintosh market when the Apple II went away".

Wozniak's favorite video game is Tetris, and he had a high score for Sabotage. In the 1990s he submitted so many high scores for Tetris to Nintendo Power that they would no longer print his scores, so he started sending them in under the alphabetically reversed name "Evets Kainzow".

In September 2000, Wozniak was inducted into the National Inventors Hall of Fame, and in 2001 he was awarded the 7th Annual Heinz Award for Technology, the Economy and Employment. The American Humanist Association awarded him the Isaac Asimov Science Award in 2011.

In 2001, Wozniak founded Wheels of Zeus (WOZ), to create wireless GPS Technology to "help everyday people find everyday things much more easily." In 2002, he joined the board of Directors of Ripcord Networks, Inc., joining Ellen Hancock, Gil Amelio, Mike Connor, and Wheels of Zeus co-founder Alex Fielding, all Apple alumni, in a new telecommunications venture. Later the same year he joined the board of Directors of Danger, Inc., the maker of the Hip Top.

In December 2005, Wozniak was awarded an honorary Doctor of Engineering degree from Kettering University. He also received honorary degrees from North Carolina State University and Nova Southeastern University, and the Telluride Tech Festival Award of Technology. In May 2011, Wozniak received an honorary Doctor of Engineering degree from Michigan State University. In June 2012, Wozniak was awarded an honorary Doctor of Engineering degree from Santa Clara University.

In 2006, he co-authored with Gina Smith his autobiography, iWoz. The book made The New York Times Best Seller list.

After seeing her stand-up performance in Saratoga, California, Wozniak began dating Comedian Kathy Griffin. Together, they attended the 2007 Emmy Awards, and subsequently made many appearances on the fourth season of her show Kathy Griffin: My Life on the D-List. Wozniak is on the show as her date for the Producers Guild of America award show. However, on a June 19, 2008 appearance on The Howard Stern Show, Griffin confirmed that they were no longer dating and decided to remain friends.

Wozniak competed on Season 8 of Dancing with the Stars in 2009 where he danced with Karina Smirnoff. Despite Wozniak and Smirnoff receiving 10 combined points from the three judges out of 30, the lowest score of the evening, he remained in the competition. He later posted on a social networking site that he felt that the vote count was not legitimate and suggested that the Dancing with the Stars judges had lied about the vote count to keep him on the show. After being briefed on the method of judging and vote counting, he retracted and apologized for his statements. Despite suffering a pulled hamstring and a fracture in his foot, Wozniak continued to compete, but was eliminated from the competition on March 31, with a score of 12 out of 30 for an Argentine Tango.

On September 30, 2010, he appeared as himself on The Big Bang Theory season 4 episode "The Cruciferous Vegetable Amplification". While dining in The Cheesecake Factory where Penny works, he is approached by Sheldon via telepresence on a Texai robot. Leonard tries to explain to Penny who Wozniak is, but she says she already knows him from Dancing with the Stars.

He was awarded the Global Award of the President of Armenia for Outstanding Contribution to Humanity Through IT in 2011.

Wozniak lives in Los Gatos, California. He applied for Australian citizenship in 2012, and has stated that he would like to live in Melbourne, Australia in the Future. Wozniak has been referred to frequently by the nickname "Woz", or "The Woz"; he has also been called "The Wonderful Wizard of Woz" and "The Second Steve". "WoZ" (short for "Wheels of Zeus") is the name of a company Wozniak founded in 2002.

On September 30, 2013, he appeared along with early Apple employees Daniel Kottke and Andy Hertzfeld on the television show John Wants Answers to discuss the movie Jobs.

In November 2014, Industry Week added Wozniak to the Manufacturing Hall of Fame.

By June 2015, Wozniak changed his mind, stating that a superintelligence takeover would be good for humans: "They're going to be smarter than us and if they're smarter than us then they'll realise they need us... We want to be the family pet and be taken care of all the time... I got this idea a few years ago and so I started feeding my dog filet steak and chicken every night because 'do unto others'".

In 2016, Wozniak changed his mind again, stating that he no longer worried about the possibility of superintelligence emerging because he is skeptical that computers will be able to compete with human "intuition": "A computer could figure out a logical endpoint decision, but that’s not the way intelligence works in humans". Wozniak added that if computers do become superintelligent, "they're going to be partners of humans over all other species just forever".

In March 2017, Wozniak was listed by UK-based company Richtopia at number 18 in the list of 200 Most Influential Philanthropists and Social Entrepreneurs.