Netflix Inc. said its original shows and movies were watched more than any other content released on the streaming service in 2019, a sign of the company’s aggressive investment in its own content in anticipation of getting fewer programs from traditional Hollywood suppliers.

The company said its most popular release this year in the U.S. was “Murder Mystery,” a comedy starring Adam Sandler and Jennifer Aniston, topping the third season of “Stranger Things.” The only program on the streaming service’s top 10 for this year...