Joyce Shepard was born on Gagarin Station in 2154 to Hannah and Rebecca Shepard, as one of twins. Her childhood was largely unremarkable; she got average grades and and only faced disciplinary actions on rare occasions, usually defending someone from a bully, or trying to keep her sister out of trouble.

When she was nine years old, her biotic abilities manifested when she was playing outdoors with her sister. Luckily, no one was hurt. The Alliance heavily suggested that Joyce be sent to Biotic Acclimation and Training, but her parents, Rebecca especially, resisted, helped by Joyce's young age. Without an implant, her abilities were negligible, but she still received some basic training from a family friend, an asari named Enlyus Kyato.

In the attack on Mindoir by Batarian slavers in 2170, Joyce Shepard’s aunt and uncle, Linda and Vincent Shepard, were killed. Per Vincent and Linda’s last will and testament, custody of their three children, Erin, Ada Henrietta, and Moira Shepard, was given to Joyce’s parents. It was a rough transition, between dealing with both grief and their household size doubling overnight, but Joyce was determined to help make it work. She spent as much time as she could with her cousins so they didn't feel abandoned.

When Joyce reached the age of eighteen, she wasn't sure what to do with her life. She had no career plans, no clear path ahead of her, so she decided to follow in her mothers' footsteps and signed up with the Alliance, receiving an L3 biotic implant.

In 2177, Joyce Shepard was a 2nd Lieutenant in charge of the marine unit that was sent to investigate lost contact with the initial pioneer team on Akuze, only for them to be attacked by thresher maws. Over the next three days, the marines made use of long-range weapons to attempt to kill them in a war of attrition, in what appeared to be a losing battle as the marines were killed one by one. Joyce fled to the landing zone after the last thresher maw fell, believing that she was the only survivor.

After Joyce’s mission debriefing, she was given six months of medical leave, with mandatory counseling. It was her surviving Akuze that first marked her as a potential future human Spectre candidate, along with an invitation to the Interplanetary Combatives Training program a year later. Her first assignment post-leave was as one of the Alliance's officers at Grissom Academy.