Haslip moved to Huntington, New York when he was four years old. At age seven, he began playing drums and then moved onto other instruments such as trumpet and tuba until playing bass at age 15. Although he took music lessons and went to a private music school, he considers himself self-taught. He has said that he went to a local music shop with his father and purchased a right-handed bass (he is left-handed) and learned to play it upside down.