PayPal did not explain the decision, but said in a statement: “We remain supportive of Libra’s aspirations and look forward to continued dialogue on ways to work together in the future.”
The US payments processing firm said it would instead focus on its own core businesses.
Facebook announced in June that it was establishing the group, with the stated aim of launching the digital currency in June 2020.
Other online giants such as Uber, Lyft and Spotify joined the Libra Association, but the proposed cryptocurrency quickly ran into regulatory issues.
France and Germany have pledged to block Libra from operating in Europe and backed the development of a public cryptocurrency instead.
Two other high-profile members, Visa and Mastercard, are also reconsidering their involvement for fear of attracting unwanted regulatory scrutiny, the Wall Street Journal reported earlier this month.
Facebook is thinking about pushing back the launch date to tackle regulatory concerns.
“We look forward to the first Libra Council meeting in 10 days and will be sharing updates following that, including details of the 1,500 entities that have indicated enthusiastic interest to participate,” the Libra Association said in tweet.
At its unveiling, Facebook said it wanted to allow people to make payments with the currency via its own apps, as well as on messaging service WhatsApp, while partner firms would also be able to accept Libra for transactions.
Paying, it said, would be as easy as texting.
But concerns have grown over how people’s money and data will be protected, as well as over the potential volatility of the currency.