The teenager, whose identity has not been revealed, appeared in Supreme court where he pleaded guilty to one count of murder and one count of attempted armed robbery in the killing of Garg.
21-year-old Garg, who migrated from Punjab, was fatally stabbed in the abdomen by assailants in Cruickshank Park in Melbourne's Yarraville while on his way to work in Jan 2010.
The teenager's friend was sentenced to 18 months probation in 2010 after agreeing to testify against the murderer in a trial and pleading guilty to accessory to murder.
The friend's plea hearing was told that he had worn a wire to record the murderer talking about the crime. The murder, which followed a series of attacks on Indians, made international headlines and provoked fear among Indian students in Australia.
The incident led to outcry in India, forcing the police authorities to solve it. The police reportedly planted a recording device at his house where the murderer's mother told her son ''I knew you did it."
The accessory agreed to wear a wire to record conversations between himself and his friend and police also installed listening devices at the accused murderer's home. In one, the boy's mother asked: "Did you do it?" Son replied: "Yeah." Mother: "Yeah, I knew you did it". Son: "I come back and I just saw him walking there. Had the biggest knife [with] me, a big silver one and I saw him." Mother: "Yeah, and you don't mention about having any knives at all if they ask you." Son: "Definitely not." The teenager was remanded in custody to appear in the Victorian Supreme Court for a pre-sentence hearing in June.