She would not reveal what her plans were after politics, saying she had no intention of seeking a diplomatic post, and neither herself or her close family were suffering ill-health, "other than a Spring cold".
It would be the Prime Minister's call when she leaves next year, she said.
"I have brought passion and pace to the portfolio, and I intend to maintain that."
Asked how Key had reacted to her decision, Parata said he respected "decision-makers", being one himself.
"I think that the work that I have been able to do can show measurable impact...I think it is part of the obligation - when you have this opportunity, you do what you can to the best of your ability, and, in my case, you then move on and leave the field clear for others who are equally or more talented."
Key said Hekia had been a strongly-performing minister who "always wanted to push the boundaries", and had overseen considerable improvements in student achievement.
He had not yet decided whether Parata would remain Education Minister until the election.
Parata was elected to Parliament in 2008 and has served as Education Minister since 2011. Her departure is unexpected - she is currently overseeing the biggest education reforms since 1989.
Her biggest achievement to date and potentially her legacy has been getting through changes to enable and encourage groups of local schools to work together, with teachers and principals paid more to take a lead in those new "communities of learning".
Not as headline-grabbing as online schools or charter school expansions, the policy isn't particularly ideological either - it is similar to an earlier policy proposal from the Post Primary Teachers Association (PPTA).
Nonetheless, significant work and compromises were made to convince the secondary school union to cautiously back a key National policy in election year (the primary school union NZEI spoke out against the reform).
Parata has had her low moments in the portfolio, with most occurring in 2012 - the year she calls her annus horribilis.
That saw an embarrassing U-turn on plans to increase class sizes, a backlash against her handling of proposals to merge or close Christchurch schools, and the implementation of the disastrous Novopay school payroll system.
There was speculation that Key would dump her from the portfolio, but he backed her and she has been pushing through a raft of changes including clearing the way for online schools (COOLs) and an overhaul of the school and ECE funding, that will scrap the decile system.
One funding proposal to give schools a "global budget" has been strongly rejected by the education unions as a return to bulk-funding, sparking classroom disruption as the PPTA and NZEI held joint meetings across the country.
The NZEI greeted news of Parata's departure this afternoon with a press release calling on Parata to drop the global budget proposal.
Labour's education spokesman Chris Hipkins said in a tweet that while he doesn't agree with much of what Parata does, "I do acknowledge her passion and commitment to education and kids".
Before entering Parliament in 2008, Parata held a number of public servant positions including in the Ministry of Foreign Affairs and Trade and advising former Labour Prime Minister David Lange during the period when Tomorrow's Schools was developed and approved.
She has two daughters of university age and is married to Sir Wira Gardiner, former director of the Waitangi Tribunal, with whom she formed a consultancy firm.
After Don Brash's Orewa speech on "special treatment" for Maori, Parata resigned her party membership and attacked the speech in a newspaper opinion piece.
She returned to the fold under John Key's leadership. Her maiden speech mentioned education five times. Three years later she took over the crucial portfolio from Anne Tolley.
Associate Education Minister Nikki Kaye's breast cancer diagnosis has seen Parata take on more work recently. Kaye would be the obvious choice to replace Parata, but for her ill-health.
New Zealand First education spokeswoman Tracey Martin - who said she was relieved for the education sector that Parata was retiring - said Kaye would have been a natural successor.
She said names being floated such as National MPs Todd Muller and Chris Bishop would be a "disaster".
"Those gentlement are from a business background...this is not a portfolio you can just shove people into."
Parata said she wasn't concerned her departure could lower the number of women in Cabinet.
"Women are fabulous creatures, and I think that the Prime Minister has an eye to the diversity of our Cabinet as well as our caucus."
Parata grew up in Ruatoria. She held today's press conference on the tiles leading in to the House, where stands the bust of another East Coast politician, Sir Apirana Ngata, also the namesake of Parata's old school.
Hekia Parata
• One of 10 siblings. Her brother and sister were brought up by relatives who were unable to have children themselves (whangai adoption).
• Involved in organising protests against the 1981 Springbok Tour.
• Quit National after former leader Don Brash's Orewa speech.
• Has been Education Minister since December 2011.
