The 51-year-old six-time major winner has not played since controversial comments about the breakaway series and the PGA Tour were published in February.
But organisers have now confirmed he will participate in the $25 million LIV Golf Invitational at Centurion Club, which begins on Thursday.
Greg Norman, chief executive and commissioner of LIV Golf, said: “Phil Mickelson is unequivocally one of the greatest golfers of this generation.
“His contributions to the sport and connection to fans around the globe cannot be overstated and we are grateful to have him.
“He strengthens an exciting field for London, where we’re proud to launch a new era for golf.”
Mickelson is one of six players added to the list of competitors for this week’s event, taking the total field to 48. The others are Itthipat Buranatanyarat, Viraj Madappa, Travis Smyth, Ian Snyman and Kevin Yuan.
Mickelson said in a statement posted on Twitter: “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.
“I needed to start prioritising the people that I love the most and work on becoming a better version of myself.
“I have spent this time with Amy and loved ones. I have been engaged and intentional in continued therapy and feel healthy and much more at peace. I realise I still have a long way to go, but I am embracing the work ahead.”
Mickelson went to explain some of the reasons why he decided to back the LIV series.
He continued: “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.
“I also love the progressive format and think it will be exciting for fans. Just as importantly, it will provide balance, allowing me to focus on a healthier approach to life on and off the course. I am incredibly grateful for what this game and the PGA Tour has given me.
“I would like to think that I have given back as well but now I am excited about this new opportunity.”
Mickelson 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 have a renewed spirit and excitement for the game.
“I am incredibly grateful for the support of my fans, partners, friends and peers and I hope in time those sentiments, relationships and support continue.”