Next year's event, which will take place in England and Wales from 30 May to 14 July, will be Afghanistan's second successive ICC Cricket World Cup after they had also featured in the 2015 tournament in Australia and New Zealand, and famously defeated Scotland by one wicket with three balls to spare in Dunedin.
The West Indies will now play in the Sunday's Super Six final and next year's 50-Over World Cup in England.
For Afghanistan, Rashid Khan picked up three wickets for 40 runs and is now just one wicket away from becoming the quickest bowler to 100 ODI wickets.
Both the teams had already qualified for the 2019 World Cup.
Afghanistan's hopes appeared dead and buried when they played poorly in the preliminaries, winning just one of their four matches to squeeze into the Super Sixes.
Afghanistan lost their first three games of the tournament and looked set to become the first of the many anticipated heartbreak stories of the tournament.
Looking ahead to the final, West Indies skipper Jason Holder said, "Obviously, it's a good opportunity to win the tournament".
Porterfield's side do have the luxury of knowing their immediate future as they prepare for their first Test match.
Son of Geelani's Successor Joins Hizbul, Pic Goes Viral on Social Media
This is the first time in the last 30 years of insurgency that a son of any top separatist leader has joined militancy. Junaid had gone missing from home on Friday, and his family had registered a missing report with police on Saturday.
"I don't think we have played the ideal game as yet".
"When we played the game against Zimbabwe we beat them with four spinners as well", the Barbadian reminded. "We've done some really good things but I don't think we have strung together the performances in batting, bowling and fielding, so that is my challenge to get into this last encounter, to end this tour on a high and win this final".
Although Scotland could have lost the match, and probably would have lost it, the odds favoured them had the match been completed.
Now Simmons is heading back to the ICC World Cup but this time with Afghanistan and said he would be working on a few surprises with his Asian outfit over the next few months in preparation for the 50-overs showpiece next year.
Hoping for revenge in the final at Harare Sports Club after two losses in the competition to the Asian side, West Indies never mounted a serious challenge, dismissed for 204 and then watching as Afghanistan strolled to their target with almost ten overs remaining.
In pursuit, Afghanistan opener and man-of-the-match Mohammad Shahzad (54) and Gulbafin Naib (45) made a solid start.
Rovman Powell top scored with 44 from number 7 but each of the top five got into double figures but only Shimron Hetmyer (38) got past 30.
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