Hearts are currently sitting in third position in the league table and are eight points ahead of fourth-placed Ross County.
Head coach Neilson had his first season in charge last year and they won the division 21 points ahead of their nearest rivals Hibernian.
Ann Budge the Hearts chairwoman told the club's official website, "I am very pleased to have secured Robbie and Stevie's services for the next two seasons, as we continue to build for the future."