Momoko Tsugunaga

In 2002, Tsugunaga auditioned for Hello! Project Kids with the song "Koi wo Shicchaimashita!" by Tanpopo. Her audition tape was aired on Morning Musume's variety show Hello! Morning. She was placed in the group with 14 other girls. In the same year, she starred in the movie Koinu Dan no Monogatari as the main character, Mao Morishita.

In 2003, Tsugunaga appeared in the music video for Miki Fujimoto's "Boogie Train '03." She also became a member of the subgroup ZYX along with Mari Yaguchi from Morning Musume, Erika Umeda, Maimi Yajima, Saki Shimizu, and Megumi Murakami. They released their debut single, "Iku ZYX! Fly High" on August 6, 2003, followed by "Shiroi Tokyo" on December 10, 2003. Later, in 2004, she participated in singing "All for One & One for All!", a collaboration single released by all Hello! Project artists under the name "H.P. All Stars."

In 2004, Tsugunaga was one of the eight girls from Hello! Project Kids were selected to form Berryz Kobo. Berryz Kobo debuted on March 3, 2004 with the single "Anata Nashi de wa Ikite Yukenai", and she was one of the lead singers of the group. From 2009 until 2014, Tsugunaga also hosted a radio show titled "Momoko Tsugunaga from Berryz Kobo's Pri-Pri-Princess."

In 2007, Tsugunaga also became part of the subgroup Buono! with Miyabi Natsuyaki and Airi Suzuki from Cute. The group formed to perform the opening and ending songs for the anime Shugo Chara! They released their first single, "Honto no Jibun", on October 31, 2007. After the show's end, Buono continued on as a side project until its disbandment in 2017.

In 2014, Berryz Kobo announced they would end activities the following year. After Berryz Kobo went on hiatus, Tsugunaga took on the role as the "playing manager" for the girl group Country Girls, a revival of a Hello! Project group formerly under the name Country Musume.

Tsugunaga majored in education and graduated in 2014.

On November 5, 2016 at Shinjuku ReNY, during Country Girls' second anniversary event, Tsugunaga announced that she would retire from the entertainment industry the following year to become a kindergarten teacher. To commemorate her graduation, a compilation CD album titled Tsugunaga Momoko Idol 15 Shuunen Kinen Album Arigatou Otomomochi (嗣永桃子 アイドル15周年記念アルバム ♡ありがとう おとももち♡, Tsugunaga Momoko Aidoru 15 Shuunen Kinen Arubamu Arigatou Otomomochi) was released on June 21, 2017, with songs selected by fan vote. Tsugunaga held her final concert on June 30, 2017 in an outdoor venue at Odaiba, exactly 15 years after her debut in Hello! Project Kids. 8,000 people attended the concert, including Berryz Kobo and Cute.