The decision means the 30-year-old will not be defending her world title at next year's athletics championships in London's Olympic stadium.
"From my first world title in Berlin 2009 to Rio 2016 I'm so fortunate to have had such an amazing career within the sport I love and this has been one of the toughest decisions I've had to make. But I know that retiring now is right," she said on Instagram.
"I've always said I want to leave my sport on a high and have no regrets and I can truly say that," added the world champion, one of Britain's most popular athletes and a familiar face in advertising.
The 30-year-old won silver at the Rio de Janeiro Olympics last August. Victory would have made her the first British female track and field athlete to win consecutive Olympic titles.
Ennis-Hill's 2012 'Super Saturday' gold medal was one of the emotional highlights of her home London Games and in the years since then, she has got married, had a son and battled with injury.
She had made clear already that Rio would be her last Olympics, but had said it would be a hard decision to miss London.
"I am in two minds about whether to call it a day and retire now or perhaps go a little bit longer," she had said in August. "I'm definitely moving to that stage of my life where things are changing."
Ennis-Hill's son Reggie was born in 2014 and although she won her world title in Beijing 13 months later, she said in the run-up to Rio that every minute away from him had to be justified.
She said there had been moments of doubt along the way as she juggled motherhood and training, wondering whether she could ever be the same athlete, and had also feared a recurring Achilles problem would prevent her from defending the title.
"I want to thank my family and incredible team who have spent so much of their time supporting me and enabling me to achieve my dreams," she said on Thursday.
Former team mate Kelly Sotherton said Ennis-Hill's departure was a sad loss for the sport.
"I imagine this decision would have been so difficult for her to make," the 2004 Olympics heptathlon bronze medallist added. "This decision is obviously the right one for her, even though it is really sad to see her go," she told Sky Sports.
(Reporting by Alan Baldwin; Editing by John O'Brien)
