A former player of renown with Ireland Schools, Colleges and 'A' team honours, O'Kelly also played club and provincial rugby with Clontarf, Lansdowne, Connacht and Munster.
He will replace Robert Forbes at the north Dublin club - Forbes had four very fruitful seasons at Suttonians' helm.
Confirming O'Kelly's appointment, Suttonians RFC President Peter Penlerrick said: "The club is delighted to have been able to secure the services of Warren for next season. Having been recently relegated to Division Three, we know that Warren has what it takes to get us straight back up to Division Two and beyond.
"As an ambitious club, with strong roots in the local community, our players, sponsors and club management know that Warren will greatly enhance our chances of achieving our ambition of going straight back up - a motto that we have all adopted for the next season."
O'Kelly will be announcing his back-room team in the coming weeks and setting out a pre-season training regime for the Suttonians players.