"We are here because Iraq wants us to be here, we are not here without the consent and without an invitation from Iraq," Stoltenberg told AFP.
"We should not stay longer than necessary, we will train the trainers as long as necessary to make sure IS [Islamic State] does not reemerge," he said.
His comments come days after the Iraqi parliament called for the government to draw up a timetable for the withdrawal of foreign troops from the country.
"The Iraqi parliament expresses its gratitude to all countries which have supported Iraq in its fight against Daesh [IS] and calls for the government to draw up a timetable for the withdrawal of foreign troops," it said in a statement.
Stoltenberg said NATO received a "written request" from Iraqi Prime Minister Haider al-Abadi to keep its troops in the country.
"We are also planning to help Iraqis to establish military schools and academies to educate their trainers to improve its capacity to form its own trainers," Stoltenberg said.
In addition, NATO will work with Iraq "on institutional reform, including fighting corruption", he added.
"The Iraqi forces in 2014 are totally different from the Iraqi forces in 2018, there was an enormous transformation," the NATO chief said.
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