Michael McDonald was charged with the murder of Breda Cummins, whose body was discovered in her Athy home.
McDonald, 48, was also charged with assaulting John Lawlor in the property.
Ms Cummins, 31, was stabbed to death in a house on Michael Dooley Terrace in the early hours of Thursday morning.
Ms Cummins, originally from the Celbridge area, had a 13-year-old son.
Mr Lawlor, who is in his 30s, was taken to Naas General Hospital for treatment. His condition is not life threatening.
McDonald, of Barnhill Road, Castledermot, Kildare, was remanded in custody and will appear at Cloverhill Courthouse on May 20.
Breda Cummin’s sister Sabrina, who visited the scene yesterday, said her mother was “heartbroken” and unable to come to her daughter’s former home.
“The pain is killing all the family. We can’t believe what some people are like, and why this happened to our sister. I don’t know what happened,” she said.
As forensic officers sealed off the house and examined the scene, gardaí carried out door-to-door enquiries. Postmortem examination results are also due to be made public.
Local councillor Mark Wall said neighbours were shocked at the death.
“Our thoughts are with the family of the woman who are bereaved,” he said. “It’s a very good area with some of the most decent people you will find in the country. It’s unfortunate that something like this has happened.”