Schildt holds both graduate and undergraduate degrees from the University of Illinois at Urbana-Champaign (UIUC). He was a member of the original ANSI committee that standardized the C language in 1989, and the ANSI/ISO committees that updated that standard in 1999, and standardized C++ in 1998.

Schildt has written books about DOS, C, C++, and other computer languages. His earliest books were published around 1985 and 1986. (The book Advanced Modula-2 from 1987 says on the cover that it is his sixth book.) His books were initially published by Osborne, an early computer book publisher which concentrated on titles for the personal computer. After the acquisition of Osborne by McGraw-Hill, the imprint continued publishing Schildt's work until the imprint was subsumed completely into the larger company. His books have sold more than 3 million copies worldwide and have been translated into "all major foreign languages".

One of Schildt's most enduring projects is the Little C interpreter, which is a lengthy example of a hand-written recursive-descent parser which interprets a subset of the C language. The program was originally published in Dr. Dobb's Journal in August, 1989 entitled "Building your own C interpreter". This example was included in the books Born to Code In C (Osborne, 1989), The Craft of C (Osborne, 1992), and in a later edition of C: The Complete Reference.

Schildt's book The Art of C++ similarly features an interpreter for a language called Mini-C++. (Mini-C++ does not support the "class" keyword, although minimal and artificial support for cin and cout has been added.) There is also a BASIC interpreter called Small BASIC in Turbo C: The Complete Reference, first edition, written in C, and another in The Art of Java (2003) written in Java.

Code for all these is available for download from the McGraw Hill technical books website, under each book.

In addition to his work as a computer scientist, Schildt is the original multi-keyboardist for the progressive rock band Starcastle, appearing on all of the group's albums, most of which were produced from 1976-1978. His style is distinguished by extensive use of Oberheim analog sequencers to create ethereal washes of sound colors, a pioneering technique which was quite cutting-edge for the pre-digital synthesizer period. He is also featured on the band's 2007 album "Song of Times."

Schildt's books have a reputation for being written in a clear style that is very easy to understand. Their technical accuracy has been challenged by reviewers, including ISO C committee members Peter Seebach, and Clive Feather, Steve Summit, author of the C FAQ, and numerous reviews in C Vu from the ACCU.