She was born in Muroran, Hokkaidō, Japan.
On August 13, 2003, she released her first single, "22 Sai no Watashi," which means "Me, 22 years old," just a few days after her 22nd birthday. Her first full-length album, Hitoribotchi, was then released on February 4, 2004, containing many solo versions of Morning Musume songs.
In August 2005, her fifth single, "Koi no Hana," which means "Flower of Love," 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 in October. 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 released a new single, "Sweet 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 October of the same year "Amasugita Kajitsu" was released, reaching 5th on the Oricon Chart, the highest place she achieved since "Koi no Telephone Goal" in 2004.
On October 5, 2008, Abe performed in an event to mark the 30th anniversary of the Sunshine City building in Ikebukuro. She was joined by other artists who were popular in the 1980s, such as Hiroko Moriguchi and Ayumi Nakamura.
It was announced on October 19, 2008, on the official Hello! Project website, that Abe will graduate from Hello! Project along with the rest of Elder Club on March 31, 2009.
On September 15, 2010, Abe released her 12th single, "Ameagari no Niji no Yō ni" (雨上がりの虹のように, "Like a Rainbow After the Rain").
In 2010, it was announced that Natsumi Abe was going to form a new group named "Dream Morning Musume" with several other former Morning Musume members.
In summer 2011, Natsumi Abe was cast in the live action drama Arakawa Under the Bridge as P-ko.
On October 7, 2007, Abe's car collided with a motorcyclist in Shibuya, Tokyo. The motorcyclist suffered minor injuries, but Abe was unhurt. She had only obtained her driver's license in July of that year.Hello! Morning (ハロー！モーニング。, April 9, 2000 – April 1, 2007)
Aiken Rosinante no Sainan ~Mukai Ryūta no Dōbutsu Nikki! (向井荒太の動物日記～愛犬ロシナンテの災難～, January – March 2001)
Nurseman (ナースマン, January – March 2002)
Angel Hearts (2002)
Koinu no Waltz (仔犬のワルツ, April – June 2004)
Takaramono (November 2005)
Arakawa Under the bridge (2012)
Hello Pro Yanen !! (ハロプロやねん !!, October 13, 2006)
Koinu Dan no Monogatari
Natsumi Abe 2004 Calendar (安倍なつみ 2004カレンダー, Released October 2003)
Natsumi Abe 2005 Calendar (September 2004)
Natsumi Abe 2006 Calendar (October 12, 2005)
Natsumi Abe 2007 Calendar (October 2006)