In 1609 she was an unknown streetwalker in the Virginia colony. Dying from syphilis only a couple of nuns would care about her. But in her last moments a powerful vampire, the Master, turned her into one of his kind. He gave her the name Darla - Dear One - and she became part of the Order of Aurelius.
Darla was 144 years old when she saw Liam in a tavern in Galway, Ireland. She thought he was magnificent and so she sired him, promising that she would show him the world. After leaving the Master to live above the ground Darla and her new mate Angelus roamed Europe and spread death and destruction wherever they went. They weren't in love, but obsessed with each other. They killed men, women and children, poets and prostitutes, lords and servants.In 1898 she offered Angelus a special gift: a Romanian gypsy girl. But when Darla saw her lover again she knew something was wrong. She could sense the filthy soul inside of him and chased him away. The gypsies were unable to take back their curse and so she killed them all (with some help from Spike and Drusilla). Two years later she met Angelus again in China. He asked her to take him back and she decided to give him another chance. But she soon realized that Angelus was trying to fool her and so she put him to the test by offering an innocent baby to him. Unable to kill the child he ran away and they wouldn't meet again for a long time.
Together with the Master Darla came to Sunnydale in 1997 where her former mate Angel was in love with a certain vampire slayer. While protecting Buffy, Angel staked Darla and she turned to dust.
But that's not the end of her story. Three years later Wolfram and Hart brought her back - as human. Following W&H's evil plans Darla tried to seduce Angel so he would eventually lose his soul. But then she had to realize that she was dying again, from the same disease that had almost killed her 400 years ago. Desperately she begged Angel to sire and save her, but he couldn't do it. Just as she had accepted her fate, Lindsey, a W&H lawyer who was in love with Darla, brought in the vampire Drusilla and she turned Darla back into an undead. 
Some time later Darla finally got what she wanted and she and Angel had a one-night stand. The result, however, was quite unexpected. A few months later she came back to LA highly pregnant. She had been unable to get rid of the child and demanded help from Angel. The child's soul effected her more and more, but she had to realize that she was unable to deliver the baby. Darla finally decided to sacrifice herself for the only living being she had ever been able to love. She staked herself and their son Connor was born.