The pair had been with a group diving off the Muglins Rock, close to Dalkey Island, but did not return to the surface as planned around 11.30am on Sunday 27 May.
The dive-boat coxswain alerted the Irish Coast Guard's Marine Rescue Co-Ordination Centre (MRCC) in Dublin which requested the RNLI all-eather lifeboat launch to assist.
Some 30 minutes after the initial call, the lifeboat spotted the two casualties together on the surface. The divers had been swept a mile-and-a-half north of the original dive site by the incoming tide.
One of the lifeboat crew entered the water to assist with their equipment and air tanks before both were taken on board the lifeboat and brought to shore. Neither was injured in the incident.
"This incident could easily have been a tragedy," said Stephen Wynne, RNLI lifeboat operations manager at Dun Laoghaire. "Fortunately the correct procedure was followed in raising the alarm early enough."