
Ireland, resuming the day on 86 for five and still 215 runs behind, showed greater resistance through the lower order but never seriously threatened to push the match into a fifth day.
They were eventually bowled out for 254 shortly after lunch, with the left-arm spin duo of Hasan Murad and Taijul Islam sharing seven wickets.
The morning's first breakthrough came when Matthew Humphreys swept Taijul straight to square leg for 16.
Andy Balbirnie and Andy McBrine then added 66 runs in the most substantial partnership of the innings, briefly quietening Bangladesh's momentum.
Balbirnie played with composure for 38 before being trapped lbw by Murad, whose persistence paid off with sharp turn from a length.
McBrine reached a fighting fifty — the third of his Test career — but his innings ended soon after the interval when he miscued a pull off Nahid Rana and offered a simple catch at midwicket.
Ireland's hopes faded from that moment. Barry McCarthy swung gamely for 25, and Graham Hume and Mark Adair chipped away at the deficit, but the outcome had long been clear.
Murad completed a four-wicket haul in only his second Test match, finishing with 4 for 60, while Taijul took 3 for 84. Rana ended with two wickets.
"He's been doing well in first-class cricket," said Bangladesh captain Najmul Hossain Shanto of Murad, who had waited long for his opportunity. "Showed what a quality bowler he is, exciting bowler."
Bangladesh's victory was forged on the weight of their first-innings total. The hosts had declared at 587 for eight on the third afternoon, securing a 301-run lead — their second-largest in Test history.
The scorecard was stacked with contributions across the top order: Mahmudul Hasan Joy's career-best 171, captain Najmul Hossain Shanto's crisp 100, and solid innings from Mominul Haque (82), Shadman Islam (80), and Liton Das (60). Only Matthew Humphreys found a way through with any consistency, returning figures of five for 170.
"Opening partnership was tremendous. Hope they'll continue," Shanto said, reflecting on the platform set by Joy and Shadman.
Ireland began their second innings in trouble almost immediately. Cade Carmichael was bowled by Rana in the fourth over, and Paul Stirling's fluent 43 ended in a mix-up that produced a sharp run-out engineered by Najmul and finished by Liton.
Taijul trapped Harry Tector for 18, and Curtis Campher departed to a flying catch from Shadman at extra cover. By stumps on the third day, Ireland were five down and still far from safety.
Bangladesh closed out the job without alarm, completing only their fourth victory by an innings margin in Tests, reports UNB.
Mahmudul was named player of the match for an innings he admitted left him "disappointed to not get the double century," though he remained "happy overall" with his contribution. "This track was pretty good to bat on, tried to keep my tactics simple," he said.
Ireland captain Andy Balbirnie was frank in his assessment. "Tough cricket for us, they were better in every aspect," he said. "We know how good they are in their own conditions. From a skill point of view, we've to get there. That'll come with more matches."
Despite the heavy defeat, Balbirnie found reasons for optimism. "Proud of how we've gone about it the last four days. The more our players are exposed to top-flight international cricket, they'll get better."
Shanto, meanwhile, dismissed suggestions that Bangladesh had engineered conditions to suit their spinners.
"Not like we want a spin wicket, we want to play on a sporting wicket," he said after the match. "All four days wicket looked pretty good."