Born on a merchant ship (CMS Marco Polo) to Noah McKnight, a former Starfleet officer and a half Klingon/Vulcan mother, Na'Toh. Amuro spent most of his life as a spacer, traveling space with his family who ran a small trading company. His mother is a half Klingon-Vulcan of a minor Klingon House. His parents weren't formally married and had in fact eloped. Klingons that know of his family called him the "bastard of a bastard" because of Klingon's stigma against inter species breeding. That didn't discourage him from spreading his "love" to other species. Having a home on a merchant ship brought him to many ports across the quadrant. He's one of adventure and free spirit. Always prefer to dive head first into action.
Amuro learned all he could about space travel, combat, and trading from his dad and his openness for the universe from his mom. He would hide his intelligence from others. Rather he prefers people underestimate him and his skills. To him, observing how people react would tell him a lot.
For a couple years, he was part of a group called the Merchant Stellar Marines, a Private Contractor Company whose services include protecting, as the name implies, merchant ships and properties. For him, it was "fun", but like many, he felt the call of Starfleet and want to be apart of something bigger than himself. Or perhaps he felt a need to make his mark on the universe.
After which, he decided to enlist in Starfleet. Enrolling at the Academy and spending years studying, though oddly joined the Federation Marines after graduation.
His hope is to find his place in the grand scheme of things and have fun while doing it.