Penelope Johnson Halliwell (later known as Grams) was the grandmother of the Charmed Ones (Prue, Piper, Phoebe, and Paige), and great-grandmother of Wyatt and Chris Halliwell.

She was a descendant of Melinda Warren, and was born with the power of telekinesis (which she passed on to both her granddaughter Pru and great-grandson Chris).

She first married Allen Halliwell, and took that last name. She gave birth to Patricia Halliwell, the future mother of the Charmed Ones.

In the sixties, Penny was good friends with Leo Wyatt. Penny was once a peace lover until Allen was killed by her former best friend, Robyn, and Robyn's warlock boyfriend, Nigel. As a result, she became a fierce demon/warlock slayer. She learned to focus her telekinetic power, and created spells and potions on her very own. She was known to be a very skilled and powerful witch, like her ancestor, Melinda Warren.

As Penny became the matriarch of the Halliwell/Warren family, she fell in love with the Necromancer Demon. But she couldn't be with him because, though he truly did love her, he used her to get to the spirits of the Halliwell/Warren line.

Penny married at least two more times, but the relationships didn't work out. When Patty married Victor Bennet, Penny didn't allow her to take his last name.

Penny witnessed the birth of Prudence, Piper, and Phoebe Halliwell, later earning the nickname 'Grams'. When Patty was forced to give immunity to a warlock named Nicholas, Grams had no choice but to bind the girls' powers, until they were ready for them.

Grams was forced to keep the secret about Patty's other daughter from her whitelighter, Sam Wilder. After Patty's death, Grams became their surrogate mother, and would continually argue with Victor about how the girls should be raised. Because of those arguments, the girls didn't see their father again for a very long time. Years later, Grams developed a heart condition. She wanted to keep the girls from receiving their powers permanently. But before she could, she died. She became a spirit, keeping watch over her grandchildren.

Grams was a high priestess and performed the marriage ceremony uniting Leo Wyatt and Piper. When their first child turned out to be a boy, Grams was upset about it, but eventually came around to accept and love Wyatt.

When Grams learned about Gideon's death at Leo's hands (because Gideon had tried to kill Wyatt), she was unsure if she could trust Leo to be around the girls.