Actor Eita was born on December 13, 1982, in Niigata Prefecture. His younger brother is actor Kento Nagayama.
Since 1999, he has been working as a model under the name "EITA," and his first magazine appearance was in Hot Dog Press. His acting debut was in the 2001 drama "Goodbye, Mr. Ozu," in which he played basketball club member Tsuyoshi Mikami. In 2002, he also appeared in the film "Blue Spring," directed by Toshiaki Toyoda.
His breakthrough came in the 2003 drama "Water Boys," in which he played student council president Masatoshi Tanaka. Since then, he has appeared in various dramas and films. He played his first leading role in the 2005 comedy film "Summertime Machine Blues," and in 2006, he was recognized for his roles in dramas such as "Nodame Cantabile," winning him the Japan Broadcasting Corporation Film and Art Award for Best Supporting Actor. In 2009, he worked on films such as "Dear Doctor," "Atsuhime," and "Last Friends," winning numerous awards including the Japan Academy Award for Best Supporting Actor.

He has also co-starred in many films with actor Ryuhei Matsuda, most recently appearing in the film "Mahoro Ekimae Kyousokyoku" as the protagonist and his friend. The two are also friends in real life, and showed great chemistry in their acting. In 2010, he married singer Kaela Kimura, and by 2013 they had two children.