Wales swept aside Belarus 3-0 with a fine performance on a bittersweet night for Jayne Ludlow's side, who cannot now qualify for the Euros.
Natasha Harding prodded Wales into the lead from close range, and Rachel Rowe doubled the advantage before half-time with a fantastic angled finish.
Jess Fishlock's cool penalty made the result safe for Wales.
However, Northern Ireland's 5-1 win over the Faroe Islands saw them pip Wales to a play-off berth.
Going into the match, Wales knew they needed to beat Belarus and hope the Faroe Islands - who had scored none and conceded 37 in their previous six qualifiers - caused an upset by avoiding defeat against Northern Ireland.
But Northern Ireland advance ahead of Wales as Group C runners-up by virtue of a better head-to-head record, despite Ludlow's side having a goal difference superior by 12.
The away goals rule favours Northern Ireland in the head-to-head calculations, after they drew 2-2 in Wales before a 0-0 draw in the return fixture in Belfast.
However, Wales will be buoyed at least by ending the campaign with a dominant victory and a good performance.
Ludlow opted to drop both of her forwards selected for the last match against Group C winners Norway. Helen Ward and Kayleigh Green missed out as Rowe and Ffion Morgan were picked.
Illness for Gemma Evans saw Charlie Estcourt given a start at left-back and Tottenham midfielder Josie Green was also recalled to form a central-defensive partnership with captain Sophie Ingle.
Incredibly, the minnows from the Faroes led in Belfast when the Wales players emerged from the tunnel, but Kenny Shiels' side were in front by the time Wales opened the scoring in Newport.
Harding had already had a shot deflected narrowly wide when she poked Wales into the lead by showing good composure in the penalty area to turn home Fishlock's intelligent pass, scoring her 19th international goal.
Fishlock, as ever, looked a threat all evening and she was pivotal to most of Wales' best moves, teeing up Ingle for a long-range shot that Nataliya Voskobovich was forced to save before her pinpoint cross was headed against the upright by Morgan who really should have opened her international account.
However, Wales did double their lead; Rowe added to the winning goal she scored in the reverse fixture with a fantastic right-footed shot from just outside the penalty area that whipped over Voskobovich.
It was no less than Ludlow's side deserved in a half where the visitors were restricted to two long-range efforts from Anna Pilipenko and Anastasiya Shcherbachenia.
Shcherbachenia, the Belarus captain, was within a whisker of getting the visitors back into things just before the hour, but her thunderbolt of a free-kick rattled the crossbar with Viktoriya Kazakevich unable to turn home the rebound.
With a comfortable advantage and the news from Belfast, the second half rather meandered along until Harding was fouled with 20 minutes remaining and Fishlock, Wales' most-capped player, fired home from the spot for her 30th international goal in her 120th appearance.
Wales might have added a fourth, but will now begin preparing to try to reach a first major finals at the 2023 World Cup.
Wales manager Jayne Ludlow told BBC Sport Wales:
"The girls stuck to the game plan, worked really hard and enjoyed themselves out there. It's been a tough, interesting campaign for us, but one that is going to make us stronger.
"There have been times where we have done excellent and got what we deserved and there have been times we haven't done those things and we will learn from those things and move on.
"As we've shown tonight, we have a great group of girls of different ages and we are looking forward to the future.
"Each campaign we are getting closer. Even points for second place this time, so we are frustrated.
"We are getting closer to making that final step and hopefully the youngsters coming through will help us do that."
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