A man has pleaded guilty to murdering his ex-girlfriend in the Belanglo State Forest, south of Sydney, and also killing her two-year-old daughter.

Key points: Karlie Pearce-Stevenson's remains were found in Belanglo State forest in 2010

Karlie Pearce-Stevenson's remains were found in Belanglo State forest in 2010 Her daughter Khandalyce's body was placed in a suitcase and left beside a South Australian highway

Her daughter Khandalyce's body was placed in a suitcase and left beside a South Australian highway Daniel James Holdom was days away from facing a murder trial

Daniel James Holdom, 43, entered guilty pleas to two counts of murder in the NSW Supreme Court just days before his trial was due to start.

Police say Holdom murdered his former girlfriend Karlie Pearce-Stevenson, stomping on her throat and leaving her body in the Belanglo State Forest in 2008.

Her remains were found in 2010 and police used DNA to identify them years later.

Police say Holdom also murdered Ms Pearce-Stevenson's two-year-old daughter Khandalyce after telling relatives he was driving her to her grandmother's house.

The child's remains were put in a suitcase, which was found on a remote highway near Wynarka in South Australia in July, 2015 — more than 1,100 kilometres from the Belanglo Forest where her mother was found.

Holdom was charged with the murders that year following a police investigation in two states.

Daniel James Holdom has pleaded guilty to murdering Karlie Pearce-Stevenson and her daughter. ( ABC News )

The mother and daughter were originally from Alice Springs.

Police say Karlie was murdered some time between December 14 and 15 in 2008.

They say Khandalyce was murdered near Wagga in NSW between December 19 and 20 in 2008.

When Holdom was committed to stand trial last year, the Director of Public Prosecutions (DPP) said there was "an overwhelming combination of circumstantial evidence and direct admissions".

Mobile phone tower records placed Holdom at both crime scenes and he also confessed to two people he knew.

Three days after Ms Pearce-Stevenson left a Canberra property with Holdom, he asked someone he knew to help clean the car before trading it in for another.

The committal hearing was also told police had an SD card from a digital camera belonging to Holdom that contained images of Ms Pearce-Stevenson's body in the forest.

Holdom will face a sentencing hearing in September.

Family believed victims were alive and well

Ms Pearce-Stevenson had not been in regular contact with her family in the lead-up to her death.

The single mother had moved away between 2006 and 2008, intending to travel and work.

NSW Police Detective Inspector Jason Dickinson holds up a photo of Karlie Jade Pearce-Stevenson and Khandalyce Kiara Pearce during a press conference in Sydney on October 21, 2015. ( AAP: Dean Lewins )

Her mother cancelled a missing person's report in September 2009 after she was reassured her daughter was safe and well, but did not want family contact.

NSW homicide squad commander Mick Willing previously said Ms Pearce-Stevenson was in "sporadic" contact with her mother, but it became less and less frequent over time until her mother died.

The extended family was under the impression Ms Pearce-Stevenson was living interstate.

A call to Crime Stoppers tipped police off that Khandalyce could be the person police found in the suitcase in 2015.