The 27-year-old and the girls – aged two and three – were killed after the blaze broke out at a first-floor apartment, next to the Grand Canal in the Clondalkin area of the city, at 2.30am.
They were treated by paramedics in the grounds of the complex but were pronounced dead at Tallaght Hospital.
A second woman, in her 30s, and a four-year-old boy were rescued from the flat on Kilcronan Avenue and are in a critical condition after suffering from smoke inhalation.
The apartment complex is used by a charity to provide short-term accommodation for women and children.
Fiona Ryan, chief executive of domestic violence charity Sonas, said: “We are absolutely devastated.
“Our sympathies and condolences are with the relatives and friends of the deceased and all those impacted by this awful tragedy.”
She added: “We are currently supporting other families in the apartment complex including those unable to return to their homes because of fire damage, for whom we are sourcing alternative accommodation.”
Sadly, we were called to a tragic fire in #Clondalkin in the early hours. Our thoughts are with the families, friends & local community.
— Dublin Fire Brigade (@DubFireBrigade) March 8, 2017
Dublin Fire Brigade said it received a number of calls about the blaze and it is understood firefighters were on the scene within five minutes.
Seven other residents at the complex – which has now been sealed off – were evacuated from their homes.
Emergency services are investigating the cause of the blaze and police have appealed for witnesses to come forward.
Inspector Ken McLaughlin, based at Clondalkin police station, said: “I’d like to express our sincere sympathies for the families of those that are involved in this incident. It’s a terrible tragedy.”
:: Several people were hurt and needed to be treated for smoke inhalation in a separate fire at an apartment complex on Dominic Street in north Dublin.