Taoiseach Leo Varadkar has paid tribute to the
As well as Mr Varadkar, the Justice Minister, opposition politicians as well as the GRA have offered sympathies to the guard's family and condemned the attack.
The officer, named as Det Garda Colm Horkan,
"I extend my deepest sympathies to the family and friends of the Garda who has died in the course of their duties," Mr Varadkar said of the guard who joined the force in the mid-1990s.
"Every day our gardaí put themselves on the frontline of crime prevention, on behalf of all of us. This requires regular acts of bravery and courage.
Sometimes the outcome is tragic and a Garda makes the ultimate sacrifice in the course of their duties.
"Our thoughts today are with all those grieving as a result of this tragic incident."
Minister for Justice Charlie Flanagan described the death of the guard as"a loss to wider Irish society".
“I am deeply shocked and saddened at the shooting of a Garda member in Roscommon last night and a full murder investigation is underway.
“The brave Detective Garda who died last night died in the line of duty, serving and protecting the community.
"His death will cause untold heartbreak to his family, loved ones and all his colleagues in An Garda Síochána across the whole country.
"It is also a loss to wider Irish society. His heroism and the debt of gratitude which we owe to him and his family will never be forgotten.
GRA President Jim Mulligan said that the detective had over 20 years experience and was a highly respected member of the force.
“On behalf of the GRA, I extend our deepest sympathy to the family of our colleague fatally shot in the line of duty in Castlerea, Co Roscommon overnight.
“Our brave colleague died as result of injuries sustained when he was responding to an incident. He was based in Ballaghaderreen, Co Roscommon, in the Castlerea District.
“A native of Co Mayo, he joined An Garda Síochána in 1995, and was an experienced detective greatly respected by colleagues.
“He is survived by his father, sister and four brothers.
“Our thoughts are with his family and colleagues at this very distressing time."
The Labour Party's justice spokesperson Seán Sherlock also condemned the incident.
"This will be a huge shock to the local community and members of our police force.
"We stand in solidarity and sadness today with An Garda Síochána. In particular, I am conscious of the profound trauma this will be to his family members, and they are in our thoughts this morning.
"The shooting of a member of An Garda Síochána is an attack on the community and I condemn those involved in this act of murder.
Fianna Fáil spokesperson for justice, Jim O’Callaghan, described the incident as "an attack on civilised society".
"We need to send out the message loud and clear that we will simply not tolerate this brutal brand of criminality against members of An Garda Síochana," he said.
The Policing Authority described the incident as "an attack on the essence and the foundations of our democracy".
"It is a fundamental assault on the principle of equality," they added. "In the midst of exemplary service to the community during the health emergency, the Garda Síochána will mourn the death of a colleague.
"On behalf of the Authority, I extend deepest sympathies to the family of the Garda and to his colleagues throughout the organisation."