Harry Potter: Every Order Of The Phoenix Member Ranked

Professor McGonagall was absent from the first Order of the Phoenix, but played a huge part in the second. Though she fought valiantly during the Battle of the Astronomy Tower, it was at the Battle of Hogwarts that she became most valuable to the team.

With the school still open after Snape and the Carrows took charge, Minerva stayed as a force of good, protecting the students where she could. When Harry returned to Hogwarts and faced up to Snape, it was the Gryffindor head that defeated the latter and dispatched of the Carrows to regain control of the castle.

From there until the finale of the battle, Professor McGonagall took charge of the defenses of the castle, animating the statues and orchestrating her fellow wizards to keep the Death Eaters outside for as long as possible. Not only did she protect the castle from threats outside, she got the younger students to safety, and neutralised any threats from students likely to turn to Voldemort.

In the books, she even dueled with the Dark Lord for a short time before his death. It's fair to say that without the loyalty and direction of Minerva McGonagall in the Battle of Hogwarts, Lord Voldemort may well have emerged victorious.