A man has been sentenced to 24 years' jail over the murder of a young Melbourne mum who was shot three times, stabbed in the heart before her throat was slit on the night of November 28, 2010.

Penelope Louise Pratt, 27, had twice called triple-0 for help on the night she was killed, telling one call-taker "trust me, you want to get to this address" after explaining she was hiding in some bushes from three men she feared were going to hurt her.

On Tuesday, Supreme Court Justice Peter Almond described the murder as "shockingly callous" as he sentenced James John Nathan Potter, 26, to a minimum of 20 years’ jail.

Ms Pratt pleaded for her life as she was shot three times in the head — twice by Potter's co-accused Aaron Gibson and once by Potter — following an argument over a $160 drug debt, the court heard.