Soul came from an extremely rich family of musicians. He had an older brother called Wes, a violinist, whom he suffered an inferiority complex to, and although he himself had a talent for playing the piano, he was reluctant to exhibit this talent because he constantly knew that Wes was better than him. After finding out that he was a Demon Weapon however, he found that he was able to escape from his family tradition as musicians and strive to become a Death Scythe instead. Evidence seems to show that he was the first Demon Weapon in the Evans family.
One day while playing the piano he was approached by Maka Albarn who had previously witnessed his ability to turn into a scythe. She asked him to become her partner and Weapon as her dream was to make a Death Scythe for Shinigami-sama; emphasizing on the word scythe, and as such had denied every possible Weapon put in front of her at DWMA. Maka also stated Soul had felt like the first person she could trust, furthermore, performing as Weapon and Meister should be figuratively easier. Soul accepted the agreement with the words 'Sure, sounds cool.' From that point on the two worked together, gathering Kishin Eggs prior to the beginning of the main story.
Soul seems to prefer to forget his past life as a musician, as he dislikes being called by his full name, including his last name, 'Evans.'