The arrest followed an appeal for information in relation to the death of Michael Stapleton, 68, from the Pinestown area of Glengoole.
It is believed he was hit by a vehicle as he walked near his home at 10.20pm on Sunday, when he may have been returning from a local pub.
Gardaí said all the indications were that he was “struck by a vehicle that failed to stop”.
Gardaí yesterday morning appealed for the driver to come forward, and a man in his 40s was arrested in the afternoon. As the investigation continued, he was detained at Thurles Garda Station under the Criminal Justice Act 1984.
The road remained closed for technical examination until yesterday afternoon, when Mr Stapleton’s remains were taken to University Hospital Waterford for an autopsy.
The person who found him performed CPR. A number of ambulances as well as gardaí arrived within a short time but he was pronounced dead at the scene. It is on the road between the villages of Glengoole (New Birmingham) and Ballysloe, close to the towns of Thurles and Urlingford.
Local Fine Gael councillor John Fahey described Mr Stapleton as “a quiet man” who “liked a couple of pints” in Brennan’s, Glengoole, from time to time. He said people walking on rural roads at night need to have the proper gear, and take no chances.
“That doesn’t excuse anyone driving away from the scene,” said Mr Fahey. “He might have been saved if someone came on him sooner, you never know.”
Inspector Padraig Powell appealed for anyone travelling between Glengoole and Ballysloe between 9pm and 10.45pm on Sunday, or anyone with recording devices on their car, to come forward.
Mr Stapleton was the seventh person to die on Irish roads in a week, bringing to 16 the number killed in July. Assistant Garda Commissioner Michael Finn said it is an extremely high-risk time on the roads, due to increased tourist and domestic traffic, and more agricultural machinery in use.
He said nearly 400 of the 102,500 vehicles monitored by safety cameras last Wednesday were over the speed limit. One driver was caught doing 139kph on a 80kph stretch of a road near Aughrim, Co Wicklow, while two others were driving at close to 90kph in 60kph zones in counties Meath and Mayo.