Kyle Lafferty opened the scoring for the hosts early on at Windsor Park to mark his 50th cap in style, before strike partners Conor Washington and Will Grigg added their own names to the scoresheet - just the second time Ireland have found the net more than once in their last 23 friendlies.
Michael O'Neill's squad, which will be cut down to 23 members on Saturday, now head to Austria for a week-long training camp before facing Slovakia in one final friendly before the real business gets underway in France on June 12.
In a match that struggled to really get going, Ireland found a way through early on when some poor defending from a Stuart Dallas cross allowed Lafferty to simply prod home just a few yards out for goal number 17 in the famous green and white strip.
It took until the 21-minute mark before another shot arrived in the low-key affair, as Chris Baird found the ball at his feet at the back post from a Steven Davis delivery, only to blast his shot into an opposition player.
Belarus's only real opening of the first half fell to Mikalay Yanush, but the top-scoring striker in the Belarusian top flight for two years running could only glance his front-post header a yard over the bar.
The Green & White Army were bossing the possession in the final third of the field, but Lafferty in particular was growing frustrated as his second shot of the evening was blocked aside in the box.
Ireland did have a second before the break, though, as another Dallas cross from the left was horribly dealt with by keeper Andrey Gorbunov, who let the ball slip through his grasp for Washington to nod home his second international goal in three caps.
O'Neill used the interval as a chance to change a few players, including the introduction of Alan Mannus, who was forced into making a simple stop down low from Syarhey Kislyak five minutes into the second half.
The visitors had gone five games, and a total of 500 minutes, without conceding a single goal heading into this Belfast clash, but the remainder of the match was mainly about Ireland prodding away.
For all their possession the Green & White Army struggled to make their dominance count, with substitute Grigg's header from a set-piece delivery being swept up by Gorbunov on the hour in a simple enough manner.
Belarus were almost given something to cheer when former Barcelona and Arsenal midfielder Alexander Hleb capitalised on fellow sub Niall McGinn's near-costly slip, although the ball got away from him and Mannus was able to clear the danger.
Ireland, now without a defeat in 11 outings stretching back some 14 months, managed to add a third late on when Grigg joined the goalscoring party following yet more slack defensive play from the visitors.
The in-form Wigan Athletic striker - who has become a cult hero at Windsor Park of late - blasted into an empty net from 12 yards out when a cross was parried directly into his path, rounding off another memorable night in Belfast for Northern Ireland.