Bendtner has signed on for the rest of 2019, writes the club on its website. It will be the first time the striker plays in the Danish Higher Division.
"I know it's a unique opportunity and I'll do everything to take advantage of it for the next four months," Bendtner writes on Instagram about the transition.
As a 16-year-old, Bendtner left Denmark for English Arsenal in 2004 and has since played for Juventus and Wolfsburg. He came to Rosenborg in 2017 and became the club's top scorer that year. But an injury stopped him from the 2018 World Cup and in November last year he was sentenced to wear a footcuff for 50 days following the mistreatment of a taxi driver in Copenhagen.
FC Copenhagen will meet Malmö FF in the group play in the Europa League this fall.