After graduating from high school, Orito went to work at a bank, but due to a recession in the economy, the bank eventually fell to restructuring, and Orito quit soon after. Orito originally found new work at the video game developer TGL composing music, but was invited by a friend from high school named Naoya Shimokawa (now the president of Aquaplus) to come work for the video game developer Leaf, which Orito accepted. Starting in 1995, Orito composed music for three of Leaf's game: DR2 Night Janki, Filsnown: Hikari to Koku, and Shizuku (precursor of To Heart). While Leaf's next game Hatsune no Naisho!! was under production, Orito quit Leaf. Orito got a part-time job working for a post office while providing outsourced musical composition for the video game developer Tactics under Nexton for the game Dōsei; afterwards, Orito was hired into Tactics where he helped compose music for two more games: Moon., and One: Kagayaku Kisetsu e.
In 1999, Orito and much of the staff who made both Moon. and One, including Jun Maeda, Itaru Hinoue, Naoki Hisaya, and OdiakeS, left Tactics to work under the video game publishing company VisualArt's where they formed the company Key. At Key, Orito has composed music for all of Key's titles, though he only contributed to a single track on the original soundtrack for Planetarian: The Reverie of a Little Planet. Music that Orito composes for Key titles is published on Key's record labelKey Sounds Label. The first album on the label, Humanity..., was produced by Orito for his temporary band Work-S. Orito was also the director for the remix albumOTSU Club Music Compilation Vol.1, also on Key Sounds Label, and is a member of OTSU, standing for the Organized Trance Sequential Unit. During his time at Key, Orito has provided outsourced musical composition for three games by three separate companies also under VisualArt's. The first was for the game Sense Off by Otherwise, followed by the game Shoya Kinjō by Giant Panda, and finally the game Realize by Playm. In 2001, Orito composed the opening and ending themes for the anime series Please Teacher!. In 2006, Orito composed the song "Precious" on Mami Kawada's debut album Seed. Between December 2007 and August 2010, Orito was one of three personalities (the others being Itaru Hinoue and another woman named Chiro working for Pekoe, another visual novel studio under VisualArt's) on an Internet radio show sponsored by Key in regards to the brand called Key Net Radio. Orito worked on Key's ninth game Rewrite with the composition of the game's music.
Shinji Orito's musical roots come from him producing dōjin music as a hobby. He used to visit a music BBS named Unison-BBS; Orito named his dōjin circle Unison Label after the website, which has since disappeared from the Internet. Many people were involved with the circle, which focused on a musical style similar to that of featured in bishōjo games. This group was in operation between 1994 and 2000, well into Orito's professional career. During the time he worked with Tactics and later Otherwise, Orito was also a member of a professional group of composers known as the Unison Sound Team; under this group, Orito was known as either "Gamma" (がんま,Ganma?) or "Gunman" (がんまん,Ganman?).