The first of two festive specials was watched by an average of 7.61m, giving the Brendan O'Carroll sitcom a 32.2% share of the audience from 10pm to 10.30pm.
It's the second year running that Mrs Brown's Boys has topped Christmas Day, although numbers were less than last year's 9.4m, representing an overall decline for all channels.
Elsewhere on BBC One, 6.98m (35.1%) saw Louis Smith win Strictly Come Dancing Christmas at 5pm. Call the Midwife attracted 6.83m (27.9%) at 7.45pm, while Doctor Who's 'Last Christmas' achieved 6.34m (27.5%) and Miranda's penultimate episode was watched by 6.67m (27.6%).
Downton Abbey's two-hour episode was ITV's biggest programme of the day outside of soaps. 5.51m (23.1%) watched from 9pm as the Crawley family celebrated Christmas, with an extra 319.9k tuning in on +1 (1.7%).
Earlier in the evening, Paul O'Grady