The 47-year-old confirmed that she wanted to exit Stamford Bridge to give more time to her family, particularly her five-year-old son Harry.
Hayes will continue at Chelsea until the end of the season and is preparing her team to face Everton in the WSL this weekend, but spent much of her pre-match press conference on Friday talking about her departure.
She said: "It was my decision. I am a mum and not many football managers sit up here and talk about that in the same way.
"It's challenging for him, I'm away at Everton, away at Real Madrid and now I am talking. This is not a selfish decision, this is a selfless decision. This is about putting first some other things in my life.
"I don't get home until quite late, six days a week. I just need to take stock. It's about work-life balance but also about having something different, more than anything else.
"I've been in post for 12 years and I've dedicated my life to this place. I've driven four hours every day, six days a week for 12 years.
"I have a five-year-old that needs more of his mummy. For sure, family matters. I have dedicated as much as I possibly can and have loved every minute of it.
"I don't think anything will come between me and the players, me and the fans. I love Chelsea, this will always be my club and I am sad on many, many levels."
Chelsea will take their time appointing Hayes's successor, with much of the club infrastructure built around her.
It will be a mammoth task to replace Hayes, who has won six WSL titles, five FA Cups and two League Cups, but the Blues boss revealed she will play her part in the search for a successor.
"I love Chelsea, this will always be my club and I am sad on many, many levels"
"[General manager] Paul Green and I have run this club since I arrived here at every juncture," she added. "It would be so Chelsea of us to succession plan our exit. Of course, I will be involved in those conversations.
"It is important to take our time to find our replacement. It's not about finding like-for-like, or anything like that, it is about identifying the needs for the team and the club. We will do that together."
Hayes will join the United States next summer. The team will be among the favourites to win gold at the 2024 Olympics in Paris.