Aidan Mullan, 35, from Tattyreagh near Omagh, died after he stumbled and fell over the wall at Burgh Quay in Dublin in the early hours of 31 July 2011.
His brother, Martin, is one of four men being honoured on Friday for trying to rescue him.
A citation says Martin Mullan's rescue bid involved significant personal risk.
The others being awarded for the rescue attempt are Dublin men Stephen Andrews, Brendan Connolly and Thomas O'Brien.
The Mullan brothers had been in Dublin to watch a GAA game.
After his brother fell into the Liffey, Martin entered the river using steps on George's Quay, and tried to swim out to rescue Aidan before he himself got into difficulties.
Mr Andrews then jumped into the water to help Martin Mullan.
He swam over to him, grabbed him and attempted to swim back to the steps on George's Quay, but he himself was pushed under the water on a number of occasions.
Mr Connolly, who was also passing by at the time, saw what was happening and went to help.
He entered the river, swam over to Martin Mullan, grabbed him, and supported him on the surface.
Mr O'Brien also entered the river and helped Mr Connolly to bring Martin back to the steps.
All four were treated at the scene by emergency services.
A short time later, the body of Aidan Mullan was recovered from the water by the Dublin Fire Brigade.
A total of 42 people are being recognised for their outstanding acts of bravery at a state ceremony at Farmleigh House in Dublin on Friday.
They include a Waterford girl who saved her cousin from a fire after a petrol bomb attack, a Cork teenager who prevented his father from being gored to death by a bull, and a police officer who rescued a woman after she jumped into the River Liffey in Dublin.
The recipients are picked by the Deeds of Bravery Council - which was established in 1947 to provide for suitable recognition by the state of deeds of bravery.
The awards will be presented by  the speaker of the DÃ¡il (Irish parliament) Sean Barrett.
"It is truly an honour to present awards to the incredibly brave individuals we welcome to Farmleigh House today," he said.
"Their courage and selflessness make them examples to us all and I believe that it is vital that such acts are recognised publically."
A County Tyrone man who tried to rescue his brother from drowning in the River Liffey four years ago is receiving an Irish state National Bravery Award.