Sporting director Joe Savage revealed the 28-year-old was the club’s No.1 target for the position following the retirement of John Murray.
He has sought to reinforce the club’s football department after joining from Preston North End and the most recent appointment is a key role which will benefit Hearts in recruitment.
Lancefield, who gained experience at Brighton & Hove Albion and Tottenham Hotspur, arrives from Premier League Southampton where he was the regional lead scout for the south of the UK.
He worked with Savage at Norwich City where he was a technical scout before the switch to St Mary’s.
Lancefield, who starts at the club today, was a recruitment analyst when he first joined Southampton and spent five years at the club.
“This is a crucial role at the club and I’m really happy that we’ve got William on board,” the sporting director told the Hearts website.
“He’s someone I know well and as such I’m well aware of his talents and the skills he will bring to this club.
“Although this was an appointment that we took a bit of time over because we wanted to get it right, as soon as I knew John Murray was departing I made William my No.1 target.
“I’m certain that in William we’ve got someone who will make a positive impact in the way that we recruit players that can take us forward on the pitch."
Murray departed Hearts after 25 years at the club in various roles.