The American hasn’t played since his biographer published controversial comments about Saudi Arabia-funded events in February.
Mickelson completed the 48-strong field in the $25m (£20m) Greg Norman-led event at the Centurion Club in St Albans. The 51-year-old had sought release from the PGA Tour to play in the event.
However, the PGA Tour has said that players participating in the event may face sanctions. In a statement on Twitter, Mickelson said it has been “humbled” to take time off from the game.
Mickelson lost several sponsors and his reputation was tarnished after he criticized the Saudi regime, yet sought to use his involvement with the series to gain on the PGA Tour.
He later missed the Masters for the first time in 28 years, as well as last month’s US PGA Championship, where he would have been the defending champion.
“First and foremost, I want to again apologise to the many people I offended and hurt with my comments a few months ago, I have made mistakes in my career in some of the things I have said and done. Taking time away and self-reflecting has been very humbling.”
Having missed the last two majors, Mickelson says he intends to play at the US Open – a major he has not won – in Brookline, Massachusetts, later in June.
He has not spoken to PGA Tour commissioner Jay Monahan, but intends to continue playing in the biggest tournament, and has said he will not resign his membership of the main tour in the United States.
He added: “I am thrilled, to begin with LIV golf and I appreciate everyone involved. I also intend to play the majors.
“I fully realise and respect some may disagree with this decision and have strong opinions and I empathise with that.
“I am ready to come back to play the game I love but after 32 years this new path is a fresh start, one that is exciting for me at this stage of my career and is clearly transformative, not just for myself, but ideally for the game and my peers.”
In an interview with the American sports magazine Sports Illustrated, Mickelson also denied suggestions his involvement with the LIV series is due to financial difficulties caused by gambling losses.
“My gambling got to a point of being reckless and embarrassing,” he said.
“I had to address it. And I’ve been addressing it for a number of years. And for hundreds of hours of therapy. I feel good where I’m at there. My family and I are and have been financially secure for some time.”