Nagayama was born in Tokyo. At the age of four, she began attending min'yo group singing lessons with her father. Although she originally went because she enjoyed the attention from her father's classmates, she soon began studying and performing min'yo together with her father. When she was ten, she started playing shamisen. Her father gave her a shamisen that she still uses today.
Nagayama continued singing and performing through her junior high school years. Her plan was to become a professional enka singer after finishing junior high school. However, when she was sixteen, her handlers told her and her parents that she was too young to sing enka. Despite her father's wishes, she then decided to become a J-pop idol singer.
Her debut song was Haru wa SA-RA SA-RA (春はSA-RA SA-RA), released in 1984. It was not well received, nor were her releases over the next two years. However, in 1986, Nagayama had her first big hit with a cover version of British girl group Bananarama's dance-pop take on Shocking Blue's Venus. Her next song, You're My Love, was also popular. Five of her songs (Venus, You're My Love, Kanashiki Koibitotachi, Heart ni Hi o Tsukete, and Hangyaku no Hero) were all Oricon top 10 hits.
In 1993, she started a second career as an enka singer. She received three prizes for her first enka song Higurashi (蜩). Suterarete (捨てられて) also became famous.
Nagayama continues to play the shamisen in many of her songs. Notable songs with shamisen parts are Jonkara Onnabushi (じょんから女節) and Usoda to Itte (噓だといって), the latter in which has been posted to YouTube under the title "DEATH BY SHAMISEN".
She regularly presents enka programmes on Japanese TV. Nagayama has had at least one song appear on the NHK program Minna no Uta. In 1993, she made her first appearance on the NHK New Year's Eve spectacular Kōhaku Uta Gassen. Since 1995, she has performed at "Kōhaku" for consecutively 13 years, making a total of 14 appearances up till date.
April 6, 2009 she announced on her blog that she has married American entrepreneur Mark Smith.
- 蜩 (Higurashi) c/w 心だけでも．．．(Kokoro Dake Demo...) 1/21/1993
- 海に降る雪 (Umi ni Furu Yuki) c/w 道しるべ (Michishirube) 6/2/1993
- なみだ酒 (Namidazake) c/w 艶花 (Tsuyabana) 9/22/1993
- 蒼月 (Tsuki) c/w あんただけ (Anta Dake) 3/9/1994
- めおと酒 (Meotozake) c/w 綾の女 (Aya no Onna) 10/5/1994
- 私が生まれて育ったところ (Watashi ga Umarete Sodatta Tokoro) c/w 硝子坂 (Garasu Saka) 1/21/1995
- 捨てられて (Suterarete) c/w ふたたびの恋 (Futatabi no Koi) 3/24/1995
- 倖せにしてね (Shiawase ni Shite ne) c/w いけない女 (Ikenai Onna) 2/21/1996
- ヨコハマ・シルエット (Yokohama Silhouette) c/w 嘘だといって (Uso Da to Itte) 6/21/1996
- たてがみ (Tategami) c/w ふられ酒 (Furarezake) 11/7/1996
- たてがみ「劇場版」 (Tategami - Gekijōban) c/w 紅い雪 (Akai Yuki) 1/22/1997
- お江戸の色女 (Oedo no Iroonna) c/w 夏ひとり (Natsu Hitori) 4/23/1997
- あの頃のなみだは (Ano Koro no Namida wa) c/w 地図のない旅 (Chizu no Nai Tabi) 4/23/1997
- ムーンライトジェラシー (Moonlight Jealousy) 11/6/1997
- 浪花夢情話（新編桂春団治） (Naniwa Yume Jōwa) 11/6/1997
- 恋のプラットホーム (Koi no Platform) c/w 洋子のズンドコ節 (Yōko no Zundokobushi) 1/13/1998
- 父さんの詩 (Tōsan no Uta) c/w 港町メルヘン (Minatomachi Märchen) 3/21/1998
- 桶屋の八つぁん (Okeya no Yatsan) c/w 新宿たずね人 (Shinjuku Tazune Hito) 5/2/1998
- 花園しぐれ (Hanazono Shigure) c/w 恋酒場 (Koi Sakaba) 11/13/1998
- 傘 (Kasa) c/w 深川恋キツネ (Fukagawagoi Kitsune) 3/24/1999
- さだめ雪 (Sadame Yuki) c/w 女の花詞 (Onna no Hanakotoba) 8/4/1999
- なみだ酒 (Namidazake) / めおと酒 (Meotozake) 12/16/1999
- 蜩 (Higurashi) / 蒼月 (Tsuki) 12/16/1999
- むすばれたいの (Musubaretai no) c/w 遠い街 (Tōi Machi) 1/1/2000
- 恋酒場 (Koi Sakaba) c/w あずさ川 (Azusagawa) 4/21/2000
- 紅い雪 (Akai Yuki) c/w 縁むすび (Enishi Musubi) 11/1/2000
- 遠野物語 (Tōno Monogatari) c/w 幾春別川 (Kishun Wakaregawa) 5/17/2001
- めぐり逢い (Meguriai) c/w やどり木夫婦 (Yadorigi Fūfu) 3/21/2002
- 艶姿女花吹雪 (Adesugata Onna no Hanafubuki) c/w 妻という名じゃなくっても (Tsuma to Iu Na Ja Naku 'tte mo) 7/24/2002
- 愛ありがとう (Ai Arigatō) c/w 色づく旅路 (Irozuku Tabiji) 10/23/2002
- 嵐峡 (Arashihazama) c/w 冬のタンゴ (Fuyu no Tango) 1/22/2003
- ありんことひまわり (Arinko to Himawari) c/w ありんこのクリスマス (Arinko no Christmas) 6/25/2003
- じょんから女節 (Jonkara Onnabushi) c/w たまゆら (Tamayura) 6/25/2003
- おんな炭坑節 (Onna Tankōbushi) 5/26/2004
- 嘘だといって (Uso Da to Itte) c/w 芭蕉布 (Bashōfu) 1/26/2005
- 洋子の・・・海 (Yōko no...Umi) c/w 洋子の・・・ふるさと (Yōko no Furusato) 6/16/2005
- 洋子の・・・名残月 (Yōko no Meizangetsu) c/w 洋子の・・・冬景色 (Yōko no Fuyukeshiki) 10/19/2005
- In 1988, she covered Johnny Hates Jazz's song "I Don't Want to be a Hero, "反逆のヒーロー".
- In 1990, she covered Diana Ross's song: "If We Hold On Together", "イフ・ウィ・ホールド・オン・トウゲザー" from the 1988 animated film, The Land Before Time.