He was arrested shortly after his mother, Siobhán Stapleton, 51, was buried.
He is being detained under section 4 of the Criminal Justice Act. Gardaí said he was arrested in the Thomastown area of Co Kilkenny and taken to Thomastown Garda Station.
Ms Stapleton, a mother of five, was found with serious head injuries in the yard of her home at Glebe Lodge in the Kilfane area, about 2km from Thomastown, last Friday.
She died in an ambulance on the way to Beaumont Hospital.
Mourners at her funeral Mass heard there was “no honest answer” why she should be taken away from her family, leaving them struggling for answers.
A huge crowd was present to pay their respects to Siobhán’s husband Peter, her son Niall — who helped carry the coffin — and daughters Deirdre, Ciara, Gráinne, and Sinéad.
The mourners thronged into the small country church at Tullahurin and spilled out into the church grounds and the adjacent roadway for the funeral of the woman.
Chief celebrant Fr John Lalor said it did not seem so long since he celebrated the marriage of Siobhán and Peter, then “a young couple embarking on a lifelong journey” together.
“They were able to build up such a good life, because of the strengths they possessed and the strength of love and respect they had for each other.”
He said Siobhán was a loving wife, a caring mother, loving daughter and sister who gave “her total energy and talents” to her marriage and the rearing of her children.
“Her love of place was evidently shown in her love of nature — gardening, wildlife, her animals, her dogs, her avid reading and interest in Irish heritage. But her loyalty was divided here between GAA and the local soccer team.”
Fr Lalor said everyone was searching for answers: Why such a wife, mother, daughter, sister, should be taken.
“We have no honest answer. But we rely on our faith in God, that he will come to our assistance and give us the hope we need to continue with our lives without the presence of Siobhán.”
After the Mass, her coffin was brought to the nearby cemetery for burial.