The 62-year-old, who has previously held coaching roles with the Tynecastle club, will work on a voluntary basis.
Hearts have been docked 15 points for next season after going into administration in June.
When asked about Brown's appointment, Locke told the club's official website: "It's an absolute no-brainer for me. It's not often you get the chance to get someone of Billy's experience and he's offered to come in and help me out during pre-season which is a magnificent gesture.
"I can't do it all on my own and it's obvious I'll need a help, so to have Billy in here is a great help.
"I can't afford to bring in an assistant and it's a measure of the man that Billy was only too willing to help out without getting paid."
Brown left his post as manager of East Fife last month.