Hilliard comes to Buffalo after spending the past two seasons coaching receivers with the Washington Redskins. He's a former NFL receiver who split 12 seasons between the New York Giants and Tampa Bay.
The Bills also hired John Anselmo to work as a special teams assistant. He previously worked under Marrone at Syracuse.
Hal Luther, also from Syracuse, was hired as assistant strength and conditioning coach.
The team announced Thursday that offensive coordinator Nathaniel Hackett will also double as quarterbacks coach.
Including Hackett, the Bills staff now features seven of Marrone's former assistants at Syracuse, where he went 25-25 over four seasons.