David Keogh grew up in a Leipzig village, when he was eight years old, he became an indentured servant. He lived in service until he was 21, at which point he was beaten to death by his master, Immortal, Roger Quinn, who found him, but treated him no better than a slave. David later met Duncan MacLeod. MacLeod was the first person who treated him decently and taught him about the world and his immortality.
In 1825, Keogh lived in Philadelphia, where he was a carpenter. Through his business, he met Julia Renquist. Her father owned the business that transported his timber. Keogh fell in love with Julia, and wanted to ask for her hand in marriage. Her father dismissed him curtly, because David was only a craftsman. Julia herself denied her love of David, because of fear of her fathers wrath. MacLeod took David away before the situation could escalate. David coped with this loss badly. He always longed to lead a normal life and be loved. He left Philadelphia shortly after these events.
In 1993, David lived north of Seacouver, where he had a small workshop and prepared his exclusive woodwork. Through his business he met and got to know Jill Pelentay, an interior decorator who consulted with him on a customer's order. The two fell in love, but when he later revealed his immortality to Jill, she could not handle it, and ended their relationship.
David refused to accept her rejection. He followed her, threatening her friends, and stalked her. Even when Jill ran over him, he refused to accept that she didn't want to be with him. He even arranged their wedding, and asked MacLeod to be his best man. Jil finally turned to Duncan for help. David confronted Jill several times, but Duncan and Richie always stood between them. He did not cease to pursue her, however, and finally broke into her home.
The completely terrified Jill, who simply saw no end to her situation, threatened suicide. Duncan intervened and almost had her back to safety but David couldn't let go, and leapt between them, causing Jill to fall her death. In his grief fueled paranoia, David thought that Duncan let Jill die on purpose and blamed MacLeod for her death. He attacked his former teacher and injured him. Duncan, however, was a far better fighter and quickly disarmed him, leaving him alive and angry.
David demanded that MacLeod kill him, but MacLeod refused to behead him. David responded by telling MacLeod that he was "coming for him", to which MacLeod responded, "Then you come for me," before throwing David's sword out of reach and walking away. David disappeared from Seacouver and his whereabouts are currently unknown.
David Keogh's sword is the same as Antonius Kalas'. Cameron Bancroft and David Robb both use Marto of Spain's Excalibur broadsword in the episodes they appear in.