"Iraq has now requested NATO support in defence capacity building," alliance head Jens Stoltenberg told regional partners at the NATO and Gulf Security conference in Qatar on Thursday.
The IS group "poses a grave threat to the Iraqi and the Syrian people, the wider region and all of our nations," he added.
IS made huge gains earlier this year, advancing to Baghdad's doorstep and stoking fears the militants might seize control of the country from the hapless Iraqi government.
A new Iraqi administration, formed under US pressure and supported by a Washington-led anti-IS coalition, has managed to hold the line, but has repeatedly asked for more help to drive IS back.
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NATO leaders at a September summit designated fighting IS a top priority for the alliance, many of whose 28 members are in the anti-IS coalition and help Baghdad separately.
"The more we cooperate, the safer we will be," Stoltenberg said, listing the need to protect vital sea lanes, energy supplies and critical infrastructure.
A NATO official said the alliance could make available its "extensive expertise in supporting, advising and assisting nations to build national defence and related security capacities."
"The allies will now review this request, in close coordination with the Iraqi authorities and with the international coalition against ISIL," the official said, using an alternative name for IS.