Masami Nagasawa was born on June 3, 1987, in Iwata, Shizuoka Prefecture, Japan. Her father, Nagasawa Kazuaki, was a professional football player who played for Japan's national team and later became a coach for Jubilo Iwata.
Masami's early start in the entertainment industry began when she won the Toho Cinderella contest in 1999 at the age of 12, making her the youngest winner in the contest's history. She then joined the entertainment business in 2000 with her film debut in Crossfire.
Masami attended the prestigious Horikoshi High School of Tokyo, a school known for producing many Japanese celebrities. Her early career involved acting in a mix of feature-length films and television dramas, as well as doing adult gravure modeling and releasing a single, Sailor Suit And Machine Gun, in which she also acted in 2006.
In addition to her acting career, Masami has also been involved in product promotion, promoting hot sauce and other products. Her impressive performance in the 2005 film Crying Out Love, In the Centre Of The World earned her the Best Supporting Actress Prize at the 28th Japanese Academy Awards, making her the youngest winner of the award at the time.
Masami's role in the 2011 film Moteki marked her arrival as an adult, and she was romantically linked to Arashi's Ninomiya Kazunari for several years. She then dated Iseya Yusuke, whom she met on the set of the 2012 film Onna Nobunaga.
However, around 2013, Masami experienced a slump in her career, but she made a comeback as a voice actress in the 2016 film Kimi No Na Wa, in which she played the role of the sexy Miki. Her performance in the film was well-received, and she became a spokeswoman for Taiwan Tourism in Japan for 2017 and 2018.
In her free time, Masami enjoys collecting stickers.