The CIA notified Austrian authorities of the scheme, which allegedly included links to the Islamic State group.
Swift's concerts in Vienna on August 8, 9 and 10 were called off by organisers after the Austrian police received the CIA's warning.
CIA Deputy Director David Cohen addressed the failed plot during the annual Intelligence and National Security Summit, held in Maryland.
"They were plotting to kill a huge number - tens of thousands of people at this concert, including I am sure many Americans - and were quite advanced in this," Cohen said.Â
"The Austrians were able to make those arrests because the agency and our partners in the intelligence community provided them information about what this ISIS-connected group was planning to do."
Austrian officials said the main suspect, a 19-year-old Austrian man, was inspired by Islamic State. He allegedly planned to attack outside the stadium, where upwards of 30,000 fans were expected to gather, with knives or homemade explosives.
Another 65,000 fans were likely to be inside the venue. Investigators discovered chemical substances and technical devices during a raid of the suspect's home.
The 19-year-old's lawyer has said the allegations were "overacting at its best," and contended Austrian authorities were "presenting this exaggeratedly" in order to get new surveillance powers.
Swift broke her silence about the cancellations last week.
"Having our Vienna shows cancelled was devastating," she wrote in a statement posted to Instagram. "The reason for the cancellations filled me with a new sense of fear, and a tremendous amount of guilt because so many people had planned on coming to those shows."
View this post on Instagram A post shared by Taylor Swift (@taylorswift)
The US pop superstar said she waited to speak until the European leg of her Eras Tour concluded to prioritise safety.
"Let me be very clear: I am not going to speak about something publicly if I think doing so might provoke those who would want to harm the fans who come to my shows," she wrote.
The main suspect and a 17-year-old were taken into custody on August 6, the day before the cancellations were announced. A third suspect, 18, was arrested August 8.
The Vienna plot also drew comparisons to a 2017 attack by a suicide bomber at an Ariana Grande concert in Manchester, England, that killed 22 people. The bomb detonated at the end of Grande's concert as thousands of young fans were leaving, becoming the deadliest extremist attack in the United Kingdom in recent years.
Cohen praised the CIA's work in preventing the planned violence, saying that other counter-terrorism "successes" in foiling plots typically go unheralded.
