The Hackney MP, who backed Jeremy Corbyn in his bid for leadership last year, said her preferred candidate for the Democrat nomination in the US presidential election was not a proud socialist like herself, but rather someone with the best chance of winning over swing voters.
"I'm glad he's run - he's had a positive effect on the race," Abbott said.
But in an interview with PoliticsHome, she gave what some considered was a surprise endorsement to Clinton instead.
"I'm backing Hillary," the MP said.
"She's proven she can appeal to a wider spectrum of the US electorate than Bernie Sanders can."
The news prompted surprise from some Labour members given criticism levelled at her ally Corbyn for being too left-wing by other MPs in the party who fear electoral oblivion in 2020.
Diane Abbott effortlessly trolling both the right and the left with this opinion, here. pic.twitter.com/eCak9VJOwc— George Melhuish (@GTMelhuish) March 4, 2016
The one time I've liked Diane Abbott. And when she wrote Christmas cards during a PLP meeting actually. Outstanding. https://t.co/7Fo0F9dg59— Andrew (@AGavinn) March 4, 2016