The two have broken up after dating for about four years, E! News has confirmed.
"Louis and Eleanor split up two weeks ago," a rep for One Direction said. "They have not announced this as they wanted some privacy during this time."
Calder has not commented.
The news comes amid recent photos posted by the U.K. newspaper The Sun that show a shirtless man resembling Tomlinson, 23, kissing another woman wearing a bikini in a pool. The outlet said the photos were taken at an "all-night party" in Bangkok, Thailand last week. He and Calder, 22, have not commented about the report.
The two began dating in 2011. Calder is also a former student of the University of Manchester. The U.K. newspaper The Daily Mail reported that Tomlinson attended her graduation ceremony last year.
One Direction fans had followed their relationship closely. While many did not support it, even sending Calder nasty tweets, some created fan pages for her and she even made appearances in fanfiction stories about the band members.
Tomlinson talked to E! News in 2013 about how Calder handled his fame and fans, calling her a "great girl."
News of Tomlinson and Calder's split also comes days after One Direction member Zayn Malik, 22, left the group's On the Road tour, amid rumors he had cheated on his fiancée Perrie Edwards, 21, based on pics of him looking cozy with a blonde in Thailand.
"I'm 22 years old... I love a girl named Perrie Edwards," Zayn posted in response. "And there's a lot of jealous f--ks in this world I'm sorry for what it looks like x."
Perrie retweeted him. A rep said Malik left the tour due to stress.