The film spin-off of the Irish comic's BBC sitcom had the largest opening day ever of an Irish film in Ireland.
It helped the film post first weekend takings of £4.3 million - just under the rest of the top five put together.
Teen drama The Fault in Our Stars fell one place to two, while comedy sequel 22 Jump Street went from two to three.
Mrs Brown's Boys D'Movie, a vehicle for O'Carroll's female alter-ego, sees the indomitable Agnes Brown embark on a campaign to save her endangered market stall.
The Universal Pictures and BBC Films co-production opened at 522 sites across the UK and Ireland, achieving an impressive site average of £8,240.
Disney fantasy Maleficent dropped one place to four, its fifth weekend tally of £819,504 pushing its overall UK and Ireland haul up to £16.5m.
In contrast, Jon Favreau's comedy Chef failed to excite audiences' palates, taking an unappetising £605,976 after two days of previews and three days on general release.
Its lacklustre performance was further highlighted by animated sequel How to Train Your Dragon 2, which managed to take a comparable amount despite only opening in Scotland and Ireland.
The DreamWorks production does not open nationwide until 11 July, though widespread previews on Saturday and Sunday gave audiences plenty of opportunities to jump the gun.
British musical Walking on Sunshine had another weekend to forget, chalking up a far from sunny three-day total of £403,490 after opening in cinemas on Friday.
Singer Leona Lewis features in the film, which uses chart hits from the 1980s in the same way 2008 success Mamma Mia! utilised the songs of Swedish supergroup Abba.
Mrs Brown's Boys D'Movie has topped the UK and Ireland box office, partly due to its record-breaking performance in star Brendan O'Carroll's homeland.