Greg Miller was a junior doctor, and was given the job of visiting Wentworth Detention Center twice a week. Most of his work was superficial, treating cuts and so on, but he knew as a junior doctor, he couldn't argue with being given that particular job.
Greg's family came to Australia, from England, and Greg had a hard time adjusting to living in a new place. Karen Travers seemed able to help him adjust as the two began a relationship, and even becoming engaged.
This engagement didn't last however, as Karen married someone else. When Karen was charged with the murder of her husband, Greg followed her trial, and knew he would see Karen when she became an inmate at Wentworth.
As a junior doctor, Greg is unable to afford to set up his own practice, something he wished to do, as most of the inmates of Wentworth only wanted to score pills off him, or medicinal alcohol in Lizzie Birdsworth's case.
Greg tried to make friends with other male colleagues who came to work at Wentworth, such as Jim Fletcher, and Paul Reid, with varying success. Greg also had a short relationship with Meg Jackson, who is uneasy about their age difference. This relationship is short lived however, Meg ends it so Greg can sort out his feelings for Karen.
After Karen's release, Greg manages to re-kindle their relationship, with Karen fearing Greg was shot during a police shootout with David O'Connell. The eventually confess their feelings, however Greg's life is in danger when David O'Connell wants revenge on Greg's involvement in the situation. Karen was shot instead, by mistake.
Greg eventually leaves Wentworth with Karen to move to Queensland, in Episode 086. When Greg returns in 107 for three episodes, he mentions that Karen has made a full recovery, the two have married, and Greg is working in a hospital and is enjoying his new life with Karen.