Seiichiro Ujiie graduated from the University of Tokyo's Faculty of Ecnomonics. Afterward, he joined Yomiuri Shimbun-sha, a newspaper publisher and the parent company of the Nippon Television Network Corp. (NTV) in 1951. Since then, he has served as the Executive Chairman, the Chairman of the Internal Audit Committee, and the Chairman of the Remuneration Committee for Nippon Television Network Corp. He has also served as an Advising Director of the Yomiuri Shinbun Holdings, which he started doing in June 2003. Ujiie has also served as a Director of Yomiuri Land Co. Ltd., which he started doing in June 1995. He has also served as the External Director at I&S BBDO Inc. Ujiie has also served as the Chairperson of the Tokyo Metropolitan Foundation for History and Culture, which had exhibits devoted to the works of such Studio Ghibli creators as Kazuo Oga and Yohei Taneda. He was also a former chairperson of the National Association of Commercial Broadcasters in Japan.

Ujiie also has production credits for both anime and live-action films. He produced most of Studio Ghibli's films and television specials, starting with the studio's 1993 television special, Ocean Waves. He is also credited with producing credits for 1994's Pom Poko, 1995's Whisper of the Heart, 1997's Princess Mononoke, 1999's My Neighbors the Yamadas, 2001's Spirited Away, 2002's The Cat Returns, 2004's Howl's Moving Castle, 2006's Tales From Earthsea, and 2008's Ponyo.

He has also produced several of the Detective Conan films, starting with 2002's Detective Conan: The Phantom of Baker Street. Ujiie also has producer credits on 2003's Detective Conan: Crossroad in the Ancient Capital, 2004's Detective Conan: Magician of the Silver Sky, 2005's Detective Conan: Strategy Above the Depths, 2006's Detective Conan: The Private Eye's Requiem, 2007's Detective Conan: Jolly Roger's in the Azure, 2008's Detective Conan: Full Score of Fear, 2009's Detective Conan: The Raven Chaser, and 2010's Detective Conan: The Lost Ship in the Sky.

Ujiie also served as a producer on the four Inuyasha films (Inuyasha the Movie: Affections Touching Across Time, Inuyasha the Movie: The Castle Beyond the Looking Glass, Inuyasha the Movie: Swords of an Honorable Ruler, and Inuyasha the Movie: Fire on the Mystic Island). He also produced the two live-action Death Note films, two Lupin III films, 2005's Black Jack: The Two Doctors of Darkness anime film, the 1990s live-action Gamera special-effects films, and the first two live-action adaptations of the Always: Sunset on Third Street (Sanchome no Yuhi – Yuyake no Uta) manga.

Sadly, Seiichiro Ujiie passed away on Monday, March 28, 2011 in a Tokyo hospital due to multiple organ failure. He was 84 years old at the time of his passing.