PewDiePie was born and raised in Gothenburg, Sweden. He was born to Lotta Kristine Johanna (née Hellstrand, born 7 May 1958) and Ulf Christian Kjellberg (born 8 January 1957), and grew up with his sister. His mother, a former KappAhl CIO, was named the 2010 CIO of the Year in Sweden. His father is also a Chief Executive of another company.

During his early schooling life, he was interested in art, and has detailed that he would draw popular video game characters such as Mario and Sonic the Hedgehog. During high school, he would skip classes to play video games at an Internet café with friends; on this topic, PewDiePie has commented, "Sweden has a great culture around Gaming." In 2008, he graduated from Göteborgs Högre Samskola. He then went on to pursue a degree in industrial economics and Technology management at Chalmers University of Technology, but left the university in 2011. On his decision, PewDiePie has stated, "Thinking about it now, it was utterly absurd. To get into Chalmers for industrial economics you need straight A's, but somehow I was happier selling hot dogs and making my own gaming-videos." While his reason for leaving Chalmers has often been reported as a want to focus on his YouTube career, in 2017, PewDiePie clarified, "Why does everyone get this story wrong? [...] I dropped out of university because I didn't like it. To drop out of university to pursue YouTube, that'd just be fucking stupid." He added that "industrial management and economics [was] boring as hell [...] [and] I couldn't relate to fucking anyone."

PewDiePie originally registered a YouTube account under the name "Pewdie"; he explains that "pew" represents the sound of lasers and "die" means death. After forgetting the password to this account, he then registered the "PewDiePie" YouTube channel on 29 April 2010. After he dropped out of Chalmers, his parents refused to support him, and as a result he funded his early videos by selling prints of his Photoshop art, as well as working at a hot dog stand. On having to work at the stand, PewDiePie stated, "the fact that I could make videos was so much more important to me than [that] I had to spend a few hours a day doing a job that wasn't that prestigious." Five years later, PewDiePie recalled, "I knew people were big at other types of videos, but there was no one big in Gaming, and I didn't know you could make money out of it. It was never like a career that I could just quit college to pursue. It was just something I loved to do. And here we are five years later and it's exploded." By December 2011, PewDiePie's channel had around 60,000 subscribers. Around the time his channel earned 700,000 subscribers, PewDiePie spoke at Nonick Conference 2012. On 11 July 2012, the channel reached 1 million subscribers, and it reached 2 million subscribers in September. In October, OpenSlate ranked the PewDiePie channel as the No. 1 YouTube channel. That December, PewDiePie signed with Maker Studios.

Kjellberg is originally from Sweden, but moved to Italy to live with his girlfriend, Marzia Bisognin. She is also a YouTube personality, formerly known on the website as CutiePieMarzia, but now known as simply Marzia. The two were introduced to each other through a friend of Bisognin's in 2011, and after establishing an online friendship, Kjellberg flew to Italy to meet her.

PewDiePie's popularity has allowed him to stir support for fundraising drives. In February 2012, PewDiePie ran for King of the Web, an online contest. He lost the overall title; however, he still became the "Gaming King of the Web" for the 1–15 February 2012 voting period. During the following voting period, PewDiePie won and donated his cash winnings to the World Wildlife Fund. He has raised money for the St. Jude Children's Research Hospital.

Aside from his own YouTube channel, PewDiePie has made appearances in the videos of other YouTube creators and series. In April 2013, he made a cameo in an episode of Epic Rap Battles of History, portraying Mikhail Baryshnikov. In July 2013, PewDiePie starred alongside Anthony Padilla and Ian Hecox of Smosh, as well as Jenna Marbles, as guest judges on the second season of Internet Icon. PewDiePie has also appeared in YouTube's annual year-end Rewind series each year from 2013 to 2016.

In December 2014, PewDiePie guest starred in two episodes of the 18th season of South Park, one of his favourite series. The two episodes served as a two-part season finale. The first part, titled "#REHASH" aired on 3 December, while the second part, titled "#HappyHolograms", aired on 10 December. In the episodes, he parodied himself and other Let's Play commentators, who added commentary over Call of Duty gameplay in an overly expressive way. In "#REHASH", the character Kyle wonders why his brother and his brother's friends favour watching others comment on events over experiencing events themselves.

Penguin Group released PewDiePie's This Book Loves You, a parody of self-help books, on 20 October 2015. The book includes a collection of aphorisms, jokes, and wisdom, paired with visuals.

The two shuffled between Sweden and Italy, before settling in Brighton, Sussex, England. Kjellberg moved to the UK in July 2013 for better Internet connectivity. Kjellberg admits that he enjoys living in Brighton, as he is able to live in general anonymity, adding that one of the reasons he has not moved to Los Angeles is, "Anytime I'm there, people are constantly patting you on the back, telling you how great you are. It fucks with your brain. I started YouTube because I was bored, not to become famous." In June 2016, Kjellberg announced he had been evicted from his recording studio after his landlord confronted him for being too loud. On 30 December 2016, he announced that he had been evicted once again, and that he had moved into Club Penguin's old UK office.

In September 2017, PewDiePie drew criticism when he used the racial slur "nigger" while live-streaming PlayerUnknown's Battlegrounds. As a response to the incident, Campo Santo co-founder Sean Vanaman referred to PewDiePie as "worse than a closeted racist", announced that Campo Santo would file copyright strikes against PewDiePie's videos featuring the studio's game Firewatch, and encouraged other game developers to do the same. PewDiePie later uploaded a short video apologizing for the language he used during the live-stream, expressing "I'm not going to make any excuses to why [the slur] did [slip out] because there are no excuses for it. I'm disappointed in myself because it seems like I've learned nothing from all these past controversies, [using the slur] was not okay. I'm really sorry if I offended, hurt or disappointed anyone with all of this. Being in the position that I am, I should know better."

On 1 March 2018, PewDiePie and Marzia announced their unisex clothing brand Tsuki via a YouTube video.