Ward's goal to make it 2-0 at Villa completed a remarkable 13 months for the Wales striker, who started the season on maternity leave.
Doncaster, who had already secured promotion to the top flight alongside the Royals, beat Millwall 4-0.
Reading's victory made it nine league wins from nine games in 2015.
For two minutes of the first half, Beth England's opening goal for Doncaster was enough to put the Belles ahead in the title race.
However, Harriet Scott's first-half strike for the Royals edged Kelly Chambers' side back in front.
Ward added a second to effectively seal the crown and Bianca Brown made it three before Alicia Robinson and Tash Baptiste hit back for Villa, while at the Keepmoat Stadium two further goals from Sue Smith and Hope Knight's effort to make it 4-0 were not enough to elevate the Belles above Reading.
Elsewhere, Everton's thrilling 5-3 win over Oxford United was enough to see the Toffees - relegated from WSL 1 last season - finish third ahead of Yeovil Town, who beat Durham 1-0 thanks to a late Corinne Yorston penalty.
Bottom side Watford held London Bees to a goalless draw in manager John Salomon's final match in charge.
Helen Ward's eighth goal in six games helped Reading beat Aston Villa 3-2 to pip Doncaster to the Women's Super League Two title on goal difference.