The alarm was raised on Sunday after a pile of clothing was found on a beach at Castlegregory.
An operation began at around midday with an all-weather lifeboat and an inshore lifeboat both involved in the search.
The search was stood down in the afternoon, with nothing found, however, at 6pm the search was reactivated at the request of Gardaí, with the two lifeboats searching the original area and the bay nearer to Tralee, assisted by Rescue 115.
At approximately 8.30pm, the volunteer lifeboat crew spotted a head above the water among a pod of dolphins about two and a half miles off Castlegregory beach.
The swimmer was conscious and immediately recovered and brought to Feint Harbour. From there, they were taken to hospital for treatment.
Feint RNLI lifeboat operations manager Gerard O'Donnell said: "After a long and exhaustive search, members of the lifeboat crew were overjoyed to sight the missing swimmer in the water.
"They had been scanning the water for any sign of movement and were worried with light fading that they would not find anyone."
Mr O'Donnell warned that even during the summer, water can be very cold, adding it was not yet known how long the swimmer had been in the water. "When the lifeboat crew found them they were a good distance from the shore and were exhausted," he said.
"We would advise that anyone undertaking a swim lets people know where they are going and when they expected back. This was a very lucky individual," Mr O'Donnell warned.
