Namekawa was born in Tokyo, and the first part of her training came at the Kunitachi University of Music there. Her principal teacher was Mikio Ikezawa. Namekawa went on to the Conservatoire de Paris, where she studied with Henriette Puig-Roget. The 1994 Leonid Kreutzer Prize helped her win admission the following year to the Musikochschule Karlsruhe in Germany, where she worked with Werner Genuit and Kaya Han and graduated with special distinction. Determined to make a career performing both traditional and contemporary repertory, she sought out further lessons with Edith Picht-Axenfeld in the former and with Pierre-Laurent Aimard (at the Musikhochschule Köln) in the latter. She had further lessons from György Kurtág, Stefan Litwin, and Florent Boffard. From 1997 to 2002, Namekawa taught piano in the German cities of Karlsruhe, Saarbrücken, and Darmstadt.
Namekawa has appeared widely in major international venues. As a soloist and chamber musician, she has performed in such venues as Carnegie Hall and Lincoln Center in New York, the Musikverein in Vienna, and the Amsterdam Concertgebouw. A frequent guest at festivals, she has appeared at the Salzburg Festival, Musik-Biennale Berlin, and the Rheingau Musik Festival, among others, and she has been a staple of radio programming in several European countries and in the U.S. Under Davies, she performed the Piano Concerto of Arnold Schoenberg and Liszt's Totentanz with the Bruckner Orchester Linz during the 2004-2005 season. In 2005, her recording debut came with Davies, on the album Music 4 Hands, featuring music by Glass and Reich, and the pairing has been especially active as the Namekawa-Davies Duo, performing new commissions from Chen Yi (the China West Suite), Joe Hisaishi (Variation 57), and several works by Glass, including Two Movements for Four Pianos (with Katia and Marielle Labèque). She released several albums in a many-volume cycle issued by the Klavier-Festival Ruhr, where she has often performed. As a soloist, Namekawa has premiered several important Glass works; in 2013, she premiered his cycle of 20 Etudes for piano solo, going on to perform it in concerts in many countries, and in 2018, she recorded the piano version of Glass's Mishima -- A Life in Four Chapters. Namekawa has often recorded for Glass's Orange Mountain Music label, issuing his Piano Sonata there in 2020. In 2022, she returned with bass-baritone Martin Achrainer for the album Philip Glass: Songs. ~ James Manheim, Rovi