The whale was beached in the Roughty River in Kenmare, about 3km inland.
It was kept alive during the low tide and eventually dragged into some water.
The whale was herded down the river by two boats and returned to open water under the supervision of County Kerry based vet Henk Offereins.
"The last sighting was of the whale swimming in a straight line towards the sea," Mr Offereins said.
"Fingers crossed it will keep swimming. Great effort from all involved."
A beached minke whale that was stranded in County Kerry in the Republic of Ireland has been helped back to safety.