The singer cited the company's recent announcement that it would compensate artists during its three-month free trial period as the reason behind her decision.
"After the events of this week, I've decided to put 1989 on Apple Music ... and happily so," she wrote. "This is simply the first time it's felt right in my gut to stream my album. Thank you, Apple, for your change of heart."
Swift, 25, also assured fans that putting "1989" on Apple Music was not because she received a special offer from the company.
"In case you're wondering if this is some exclusive deal like you've seen Apple do with other artists, it's not," she added.
Earlier this week, the "Style" singer wrote a Tumblr post criticizing Apple for not paying royalty-holders during the trial period of Apple Music. Almost immediately thereafter, Apple announced that it had changed its policy.
"When I woke up and read Taylor's note, it solidified quickly that we needed a change," Apple executive Eddy Cue told Rolling Stone. "Music is a big part of our DNA and we always strive to make sure artists are paid for their work."