One of the men was caught on CCTV leaning over to watch as the victim entered her PIN while buying groceries at Waitrose in Wandsworth, south-west London.
He is then seen recording the code in his phone as the unsuspecting pensioner leaves the store.
An accomplice lying in wait outside the shop allegedly distracted the elderly woman by posing with a map pretending to be lost, allowing another to take her card from her pocket.
The thieves then went on a spree totalling £21,000, buying clothes, six second-hand cars, and fast food meals, according to police.
“The money was the victim’s life savings that she was keeping for her grandchildren,” a Metropolitan Police spokesman said.
“The theft has also had a significant impact on the victim, leading her to change her usual routine.”
No arrests have been made.