Natsumi Abe was born in Muroran, Hokkaidō Prefecture, Japan. Her nickname is Nacci or Nacchi. Her younger sister, Asami Abe, is also a J-pop singer.
Abe was one of the first members of the group chosen in 1997. She was also the lead girl for many of the singles especially before Maki Goto joined, most notable in "Furusato" where all the other girls sang harmonies/back-up only. Abe has had a few solo songs including the theme for a commercial she was in, and "Otoko Tomodachi" from Morning Musume's 4th album Ikimasshoi!. She also has lead roles in Morning Musume productions like their play, Love Century and their movie, Pinch Runner. Abe also has done quite a bit of acting in television dramas such as Nurseman.
Abe has never been a part of a Morning Musume subgroup but has led each shuffle group she has been in. She was also the lead of Morning Musume Sakura Gumi until her graduation at the end of the Hello! Project Winter tour on January 25, 2004.
She released her first single, "22 sai no Watashi", on August 13, 2003, just a few days after her 22nd birthday. Her first full length CD was released shortly afterwards, containing many solo versions of Morning Musume songs.
At one time, Abe was the most popular member of Morning Musume, and many songs featured her as a lead singer. However, it wasn't until the summer of 2003 that Abe officially went solo. She graduated not too long after that, in the early winter of 2004, to continue on with her solo career. She continued to release more singles while actively participating in other Hello! Project activities such as concerts, the special soloist group Nochiura Natsumi with Aya Matsuura and Maki Goto, and the Hello! Project super shuffle unit song "All for One & One for All", sung together with all other soloists and groups within Hello! Project at the time.
In late 2004, there was a plagiarism scandal with some of her essays and poems in her photobooks which were copied off works by other artists, and she took personal leave for three months. During that time she ceased participation from all H!P-related activities, including Kaori Iida's graduation concert in January 2005. As a result, an album scheduled for release in early 2005 was canceled. A single named "Nariyamanai Tambourine" that was supposed to be released on January 26, 2005 was also canceled (instead, "Yume Naraba" took its place in April 2005). She returned in February 2005, and has been participating in Hello! Project activities once again, most notably the Nochiura Natsumi's tour.
In August 2005, her fifth single "Koi no Hana" was released, and she also became a member of the Hello! Project special unit DEF.DIVA together with Maki Goto, Rika Ishikawa and Aya Matsuura. The single "Takaramono" was also released in November credited as "Sen", who is the main character of the drama "Takaramono", played by Abe. In the spring of 2006, Abe had a new single "Sweet-o-holic", together with a new album "2nd~Shimiwataru Omoi". June 2006 saw Abe release "The Stress," a cover of the 1989 song by pop idol Chisato Moritaka.
In 2006, Natsumi and her sister, Asami Abe, will be playing the title roles in a Japanese TV drama about the 60's Japanese pop duo The Peanuts. (Ironically, Natsumi's former Morning Musume bandmates Ai Kago and Nozomi Tsuji have recorded cover versions of several Peanuts songs in their post-Musume group W (Double You).)
In late June 2006, some time after the release of "ecru", online hate campaigns were started against Abe because she was accused of killing a national treasure tortoise in the DVD making of. The making of doesn't show her even touching the tortoise. It was moved, but it was done by the production staff, not Abe herself. Most people consider this just another attempt by media to make another scandal. Abe herself has refused to make comments and it has not affected any of her Hello! Project-related activities.
In October of the same year "Amasugita Kajitsu" was released and reached 5th on the Oricon Chart, the highest place she achieved since "Koi no Telephone GOAL" in 2004.
In early 2007, Abe was chosen to be a member of Morning Musume Tanjō 10 Nen Kinentai (モーニング娘。誕生10年記念隊, Morning Musume Tanjō 10 Nen Kinentai?) - a unit created to celebrate Morning Musume's 10th anniversary as a group. Morning Musume Tanjō 10 Nen Kinentai also consists of Kaori Iida, Maki Goto, Risa Niigaki and Koharu Kusumi. Their song, Bokura ga Ikiru MY ASIA (僕らが生きるMY ASIA, Bokura ga Ikiru MY ASIA?), will be released on January 24, 2007.