They booked their spots at the tournament following the second day of competition at the Regional Qualifier – Europe in Perth, Scotland last week.
Northern Ireland secured their qualification with a resounding 57-42 victory over Wales, looking comfortable as they outclassed their opposition.
Scotland’s 52-40 victory over Wales on Friday evening meant they took the second place available for the Europe region, with heartbroken Wales missing out after failing to win either of their two matches.
Northern Ireland and Scotland will join England, who qualify automatically as host nation, at the tournament, along with Australia, New Zealand, Jamaica, South Africa and Malawi, who all qualified through their rankings.
Speaking after their victory, Northern Ireland’s captain Caroline O’Hanlon said: “There was a lot at stake - both teams were playing for their lives today really so I’m just relieved to get over the line.
“We knew if we went hard and played to our potential that we would get a result but Wales are a great team and we knew they’d put it up to us right to the very end.”
The remaining eight teams must book their places at the showcase event through regional qualifying tournaments in the remaining four regions – Africa, Americas, Asia and Oceania.
The Cook Islands will compete in the Oceania qualifiers in Auckland in April for a place in the 16-team World Cup.
The side will take on the likes of Fiji, Samoa and Papua New Guinea at the tournament from April 17 to 22.
The final list of qualified teams will be confirmed officially by the INF in September 2018.