Kamiya is of Japanese, Portuguese and Italian descent.^[8] He was born in Brazil, spent his childhood in Brazil, and moved to Japan at the age of 7^[9] where he lives currently.^[10] His legal nationality is Brazilian.^[11]

In elementary school, he was bullied due to being a foreigner, and in junior high school he did not go to school and played video games instead. In high school, he started drawing and began working in dо̄jin, but for his first dо̄jinshi sales event, he sold zero copies.^[12] However, at the request of an industry insider who saw his dо̄jin magazine, his color illustrations and manga were published in the 3rd volume of the MELTY BLOOD Anthology, making his commercial debut while still in high school.

In November 2005, Kamiya appeared in Dengeki Comic Gao! with his series E.A.r.T.h, making his official mangaka debut. This series finished with 4 volumes in April 2008.

In February 2008, he began publishing Gurīdo Paketto ∞ in ASCII Media Works's Dengeki Maoh magazine. Gurīdo Paketto ∞ has been in an indefinite hiatus since August 2011 since Kamiya was diagnosed with stomach cancer in May of the same year.^[13]

In November 2008, he started illustrating for the light novel series A Dark Rabbit Has Seven Lives by Takaya Kagami. This series became a hit and was made into an anime in July 2011.

In April 2012, Kamiya started publishing the light novel series No Game, No Life which he wrote and illustrated himself. The series was a success and an anime adaptation was announced in July 2013, which aired from April to June 2014.

In April 2013, Kamiya's second light novel series Clockwork Planet, in joint authorship with Tsubaki Himana, began publishing.

Both No Game, No Life and Clockwork Planet have been adapted to manga with Kamiya writing and Mashiro Hiiragi illustrating. According to Kamiya, this is his "de facto return" to the manga business.^[14]

When discussing the origin of his pen name, he said he liked the sound of "Kamiya" and wanted 神谷 (Kamiya) to be his surname, however Kamiya said that he was afraid to call himself using these kanji so he split the name into two parts, "Ka" and "miya." He then converted each portion with his eyes closed for a few seconds before landing on "榎" (Ka) and "宮" (miya) respectively. As for "Yū" (祐), Kamiya believes he took it from the name of the main protagonist of Kanon, Yuichi Aizawa, which he was passionate about at the time.^[15]

His style of illustration is often called Kamiya-nuri (榎宮塗り, lit. Kamiya-coating), which describes the vivid rainbow-coloring his illustrations usually have.

Kamiya initially worked as an illustrator, but later focused on being a mangaka. When his first light novel illustration job, Iregyrāzu Paradaizu, was terminated for undisclosed reasons, he wanted to try his hand at manga where he alone was responsible for everything. For this reason, Kamiya rarely takes many illustration jobs for light novels and is also why he has turned down manga adaptation job offers.^[16]

He is a fan of the Touhou Project series of games, many illustrations present on his official website of characters like Suwako Moriya^[17] and Flandre Scarlet.^[18]

In May 2011, Kamiya was diagnosed with stomach cancer.^[13] He was discharged from the hospital in August and is still undergoing treatment for cancer prevention. After the diagnosis, he decided to focus on writing light novels due to it being more compatible with treatment.

In August 2011, Kamiya married his manga assistant, Mashiro Hiiragi. On May 7, 2015, it was reported that he and Mashiro Hiiragi had a child together.^[19]

• Official website (in Japanese)