Ceirdwyn was born in Eastern Celtic Britain in 29AD. She grew up to become a warrior and fought against the Romans. In 60AD, she died while fighting the Romans in Boudicca's army and became Immortal. She soon meets her first teacher Roman General Marcus Constantine who teaches her about her heritage. Marcus quickly fell for the beautiful woman and convinced her to come with him to Rome.The two lived together until 73 AD when Ceirdwyn decided to follow her own path of Immortality. She later returned to her native Britain and meets her first Pupil Alex Raven in 75 AD. In 1255 she later meets her second student Mathew of Salsbury(Matthew McCormick).
In 1746, Ceirdwyn under the alias Flora McDonald is in Scotland. While there she meets Bonnie Prince Charlie who is in the company of Fellow Immortal Duncan MacLeod. After seeing Charlie to freedom, Macleod went on a rampage of his own against the English until Ceirdwyn managed to bring him back out of his bloodlust.In the 1980s, She meets a mortal man named Steven Jarmel whom she fell in love with and told him about Immortals and the two get married in 1983. The lived happy together but their happiness would be shattered. In 1995 after leaving a restaurant, Ceirdwyn and her Husband Steven are gunned down by armed thugs trying to mug them. Donning her Celtic warpaint and carrying her Celtic sword, she goes after the punks that killed Steven. Ceirdwyn manages to kill the one who pulled the trigger and goes after the rest. Fortunately for the punks Duncan MacLeod manages to find her and convince her to let go of her bloodlust just as she told him many years ago. she reluctantly agrees. But the gang has plans to kill her. They break into her house but she is able to fight them off. She still lets them go.