Mary O'Leary is a shopkeeper who resides on Craggy Island with her husband John. Although they appear to be a loving, happy couple in front of Ted and Dougal they actually hate each other and are always trying to kill each other. She was portrayed by Irish actress Rynagh O'Grady.
The following is a list of incidents involving the couple by the order of episodes they appear in:
- They are seen arguing with each other at Funland before Ted shows up
- They meet the priests at the hospital after Paul Stone is admitted following his lightning strike. Mary is on crutches having "sprained" her ankle while John is wearing a bloodied bandage but passes it off as Mary having knicked him with a knife and not stabbing him. After they leave, she kicks him in the shins
- They argue with each other in their shop before Dougal arrives to purchase a pair of handcuffs
- Mary tries to drown her husband in a bucket of water before the priests arrive but John passes it off as Mary just washing his hair
- They bring the priests a gift of chocolate Easter eggs to the parochial house and are arguing before Ted answers the door
- John locks Mary in a large wardrobe in their shop and throws away the key