The Men in Green take their place in the showcase tournament for the sixth time after Canada fail to leapfrog them on net run-rate
Ireland have joined Papua New Guinea in securing direct qualification for the Men's T20 World Cup in 2020.
The Men in Green finished in top spot in Group B in the qualifying event in the United Arab Emirates to confirm their place.
Gary Wilson's side won four and lost two of their group matches to finish locked on eight points eight Oman.
But their superior net run-rate saw them claim the second of the six remaining places at the World Cup in Australia next year.
Oman and Canada will now go through the play-off system in an effort to secure a spot.
Earlier on Sunday, Papua New Guinea confirmed their place in their first-ever World Cup after finishing top of Group A.
The event in the UAE offered six places in the 16-team World Cup scheduled for October and November next year.
The remaining berths will be determined during the final week of the qualifier, which gives sides who missed out on a direct place a second chance.