Moody, during his time as an Auror, served the Ministry of Magic, fighting Death Eaters under Lord Voldemort's command. He was a key member of the Order of the Phoenix, led by Albus Dumbledore, in the struggle to defeat Voldemort, and his efforts were said to have led to half the cells in Azkaban being populated by Death Eaters he captured.

As the war continued, and the situation grew more fraught, the Ministry of Magic authorised their Aurors to use Unforgivable Curses against Death Eaters, a practice which continued for a time after Voldemort's fall from power. Moody was known to have killed a number of Voldemort's followers (including Evan Rosier) however he avoided doing so where possible.

At some point during his life, Moody violently tore apart a birthday present, paranoid that it may be a cleverly disguised Basilisk egg. It turned out that it was only a carriage clock, though it is unknown if he rectified his mistake.

It is believed that his activities during the First Wizarding War and his time as an Auror that led to Moody losing a leg (replaced by a wooden prosthesis) and an eye (replaced with a magical prosthesis). His work also led to significant facial scarring, including losing a piece of his nose in his fight with Evan Rosier.