It will be 24-year-old O'Callaghan's first Test start after winning all eight of his previous caps off the bench. He teams up with Munster second-row colleague Paul O'Connell.
Maggs and O'Kelly drop down to replacement duty, and there is no place in the 22 for Munster wing Anthony Horgan, who went on as a second-half substitute in Paris.
Ireland are bidding for a fifth successive victory over Wales.
Ireland team to play Wales in the RBS 6 Nations Championship at Lansdowne Road, Dublin: G Dempsey (Leinster); S Horgan (Leinster), G D'Arcy (Leinster), B O'Driscoll (Leinster, capt), T Howe (Ulster); R O'Gara (Munster), P Stringer (Munster); R Corrigan (Leinster), S Byrne (Leinster), J Hayes (Munster), D O'Callaghan (Munster), P O'Connell (Munster), S Easterby (Llanelli Scarlets), K Gleeson (Leinster), A Foley (Munster).
Replacements: F Sheahan (Munster), S Best (Ulster), M O'Kelly (Leinster), V Costello (Leinster), G Easterby (Rotherham), D Humphreys (Ulster), K Maggs (Bath).
As head coach Stuart Lancaster polishes the axe he will soon wield over his World Cup training squad, Exeter Chiefs coach Rob Baxter has backed Jack Nowell, Henry Slade and Luke Cowan-Dickie to be given a stay of execution.
Italy Under-20s held off a late Samoa blitz to retain their place in the World Rugby U20 Championship on Saturday and head coach Alessandro Troncon believes the experience will have served as a valuable lesson for his young troops.