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.

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.

He has pleaded guilty to murdering his former girlfriend Karlie Pearce-Stevenson and also to murdering her two-year-old daughter Khandalyce.

Police say Holdom murdered Ms Pearce-Stevenson and left her body in the Belanglo State Forest in 2008, stomping on her throat and then leaving her body there.

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

Police say Holdom also murdered Karlie’s daughter Khandalyce after telling relatives her was driving her to her grandmother’s house.

The child’s remains were put in a suitcase which was found on a remote highway in South Australia in July, 2015.

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

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.

Holdom will face a sentencing hearing in September.

-ABC