Usual wife of Cúchulainn and daughter of Forgall Manach [the Wily] of Lusca [Lusk], in what is now north Co. Dublin; Cúchulainn's other wife is Eithne Ingubai, who may be confused with Emer. Conventionally described as a female paragon, she possessed the six gifts of womanhood: beauty, voice, sweet speech, skill in needlework, wisdom, chastity. Her sister was Fial (2) and her three brothers Scibar, Ibor, and Cat. Although Cúchulainn is smitten with Emer, and she with him, as soon as he comes to her father's fortress and beholds her, Forgall refuses his demand to marry her. As recounted in Tochmarc Emire [The Wooing of Emer], Forgall objects to Cúchulainn as a suitor for two reasons. His elder daughter, Fial, has to be married first, and more importantly, he feels the future hero of Ulster has not yet acquired a sufficient reputation and needs more training. He further suggests that Cúchulainn seek training with the warlike Domnall Míldemail in Alba [Scotland]. Domnall in turn tells Cúchulainn that his training would be best completed under the female warrior Scáthach, also in Alba, with whom the Ulsterman stays a long while. In the mean time Forgall tries to persuade Lugaid mac Nóis, a Munster king, to marry Emer, but he refuses the opportunity, fearing reprisals from the powerful Cúchulainn, who is, in addition, his foster-brother.
When Cúchulainn returns from Alba, eager to claim Emer, Forgall refuses him and locks him out of his fortress of Lusca. In a salmon-leap Cúchulainn scales the wall and slaughters twenty-four of Forgall's men before he, in despair, jumps from the ramparts to his death. Cúchulainn then joyously departs with Emer, her foster-sister, and two loads of silver and gold. An ally of Forgall's, Scenmenn, tries to stop them, but Cúchulainn dispatches him quickly at a ford on the Ailbéne river, known later as Áth Scenmenn [Scenmenn's Ford]. Twice a victor, his prowess tested, Cúchulainn takes Emer to his fortress home of Dún Delgan [Dundalk].
Their married life is not always blissful, for Cúchulainn loves many women, and still more love him. The most threatening of these affairs, causing the only jealousy of Emer, is with Fand, wife of Manannán mac Lir, as told in Serglige Con Culainn [The Wasting Sickness of Cúchulainn]. After the adulterous pair have spent a month in lovemaking, Emer decides to kill her rival Fand. She finds their hidden trysting spot, but when she sees how much Fand loves Cúchulainn, she decides to give him up to her for the greater good. Fand, however, deeply impressed by Emer's magnanimity as well as her love, decides to return to her own husband, Manannán. And magically the affair vanishes from memory. Manannán shakes an enchanted cloak, ensuring that Fand and Cúchulainn never meet again; and Cúchulainn and Emer take potions of forgetfulness. In another story, Fled Bricrenn [Briccriu's Feast], Emer bears the epithet Foltchaín [of the fair hair] and arrives in the company of fifty women, seeking entrance to Briccriu's palace.
Cúchulainn has a vision of Emer's death before his own. He dreams that Emain Macha is in flames and that she is thrown from the ramparts. But when he rushes home he finds her well and safe, although cautious of the dream's foreboding. He nevertheless returns to the road that will lead to the Pillar Stone and his own death. Emer then joins him in the grave.