Gardai have launched a murder investigation this evening after a post-mortem confirmed the man sustained severe injuries to his head and upper body.
The victim, aged in his mid-60s, was named locally as Thomas (Toddy) Dooley.
Mr Dooley was the father of three grown-up children.
Mr Dooley's body was discovered on the couch at his home on Sister Senan Court in Edenderry, Co Offaly, at about 2.45pm yesterday. He had not been seen for some time and concerned neighbours had contacted gardai, who discovered his body on the couch in his living room.
A family liaison officer has been appointed and an incident room has been established at Tullamore Garda Station.
Gardai were treating the death as suspicious last night, confirming "it's not a sudden death".
A source said Mr Dooley suffered head injuries and the investigation would likely be upgraded to murder today pending the results of a post-mortem that was due to get under way this morning.
Mr Dooley's body remained in situ at his home last night pending the results of the examination.
The house was sealed off and the Office of the State Pathologist was notified yesterday as a forensics team immediately began combing the area for evidence. There was no sign of a forced entry but a back window in the house was open.
Shocked neighbours said they were stunned to hear of Mr Dooley's death.
A neighbour, who lives near Mr Dooley's council estate, described him as "an inoffensive character" who lived alone and had cared for his elderly mother who did not live with him.
An Edenderry native, Mr Dooley was well known in the area.
Local Cllr Finian O'Neill (FF) described him as "a quiet guy".
"He wouldn't mind anyone – would stick to himself," he told the Irish Independent.
"He lived in Edenderry all his life," he said, adding, "he'd always have an aul hello for everyone."
Gardai were alerted to the grim scene by a neighbour who said they were concerned about Mr Dooley's welfare.
On arrival at the house, gardai discovered a rear window open and "found a male lying on a couch with head injuries".
Cllr Fergus McDonnell (Ind) said Mr Dooley was married many years ago but had separated.
"He was a very quiet, inoffensive fella," he recalled.
Gardai are appealing to anybody who may have seen anything suspicious in the area of Sister Senan Court to contact Tullamore garda station on (057) 93 27600 or ring the Garda Confidential Line on 1800 666 111.
Meanwhile, gardai have launched a murder investigation into the death of a 26-year-old Latvian man in Co Laois on Saturday.
The move follows the results of a post-mortem on the body of the man who was found at a house in Spa Street, Portarlington, Co Laois, at about 5pm on Saturday.
Gardai confirmed last night that the investigation has been upgraded to murder.
The post-mortem was carried out at the Midland Regional Hospital in Tullamore, Co Offaly, following a preliminary examination at the scene.
Two Lithuanian men, one in his early 30s and another in his mid-40s, were arrested at the scene.
The men are being held in Portlaoise and Tullamore garda stations.
Gardai were last night deciding whether to release or charge the men. It is expected one of them will appear in court in connection with the death today.
It is understood the deceased had been living at the property with one of the men.
A row is believed to have taken place while the three were drinking at the property.
Allison Bray and Eoghan MacConnell