The IMDb originated from two lists started as independent projects in early 1989 by participants in the Usenet newsgroup rec.arts.movies. In each case, a single maintainer recorded items emailed by newsgroup readers, and posted updated versions of his list from time to time. The founding ideas of the database began with a posting titled "Those Eyes", on the subject of actresses with beautiful eyes. Hank Driskill began to collect a list of attractive actresses and what movies they had appeared in, and as the size of the repeated posting grew far beyond a normal newsgroup article, it soon became known simply as "THE LIST". (The first code to manage this list was a Perl program written by Randal L. Schwartz to "invert the list", organizing the list by movies instead of actresses.

The other project, started by Chuck Musciano, was briefly called the "Movie Ratings List" and soon became the "Movie Ratings Report". Musciano simply asked readers to rate movies on a scale of one to ten, and reported on the votes. He soon began posting "ballots" with lists of movies for people to rate, so his list also grew quickly.

In 1990, Col Needham collated the two lists and produced a "Combined LIST & Movie Ratings Report". (His first posting of the database scripts is not available.) Needham soon started a (male) "Actors List", while Dave Knight began a "Directors List", and Andy Krieg took over THE LIST, which would later be renamed the "Actress List". Both this and the Actors List had been restricted to people who were still alive and working, but retired people began to be added, and Needham also started what was then (but did not remain) a separate "Dead Actors/Actresses List". The goal now was to make the lists as inclusive as the maintainers could manage. In late 1990, the lists included almost 10,000 movies and television series. On October 17, 1990, Needham posted a collection of Unix shell scripts which could be used to search the four lists, and the database that would become the IMDb was born. At the time, it was known as the "rec.arts.movies movie database".

By 1992, the database had been expanded to include additional categories of filmmakers and other demographic material, as well as trivia, biographies, and plot summaries; the movie ratings had been properly integrated with the list data; and a centralized email interface for querying the database had been created. Later in the year, it moved onto the World Wide Web (a network in its infancy back then) under the name of Cardiff Internet Movie Database. The database resided on the servers of the computer science department of Cardiff University in the UK. Rob Hartill was the original web interface author. In 1994, the email interface was revised to accept the submission of all information, meaning that people no longer had to email the specific list maintainer with their updates. However, the structure remained that information received on a single film was divided among multiple section managers, the sections being defined and determined by categories of film personnel and the individual filmographies contained therein. Its management also continued to be in the hands of a small contingent of underpaid or volunteer "section managers" who were receiving ever-growing quantities of information on films from around the world and across time from contributors of widely varying levels of expertise and informational resources. Despite the annual claims of Needham, in a year-end report newsletter to the Top 50 contributors, that "fewer holes" must now remain for the coming year, the amount of information still missing from the database was vastly underestimated. Over the next few years, the database was run on a network of mirrors across the world with donated bandwidth.

The website is Perl-based.

In 1995, it became obvious to the principal site managers that the project had become too large to maintain merely through donations and spare-time efforts. The decision was made to become a commercial venture. In 1996, IMDb was incorporated in the United Kingdom, becoming the Internet Movie Database Ltd. Col Needham became the primary owner as well as the identified figurehead. The section managers were offered "shares" in the company in exchange for the amount of work-time they put in, and sometimes also for their monetary donations. A couple of these went to work full time for salary. (Needham had already been drawing one.) General revenue for site operations was generated through advertising, licensing and partnerships.

This state of affairs continued until 1998. The database was growing every day. It was again reaching a critical point in terms of quantity of new data received versus number of personnel available. There was an urgent need for more full-time managers, who would of course want to be paid. Most revenues were being spent on equipment. The system was also suffering noticeable slowdowns both in accessing the site and in having new data posted. Offers were solicited from academic institutions, but none were interested. Private enterprises with interests in the entertainment industry were also solicited, and from some of these offers were forthcoming to purchase IMDb. However, the shareholders were unwilling to sell without guarantees that the information would be accessible to the internet community for free. None of this activity was made known to the several hundred volunteers who were contributing the vast majority of information now coming in to IMDb.

In 1998, Jeff Bezos, founder, owner and CEO of Amazon.com, struck a deal with Col Needham and other principal shareholders to buy IMDb outright and attach it to Amazon as a subsidiary, private company. This gave IMDb the ability to pay the shareholders salaries for their work, while Amazon.com would be able to use the IMDb as an advertising resource for selling DVDs and videotapes. Volunteer contributors were not advised in advance of even the possibility of IMDb—and their contributions along with it—being sold to a private business, which created some initial discord and defection of regulars.

IMDb continued to expand its functionality. In 2002 it added a subscription service known as IMDbPro aimed at entertainment professionals. It provides a variety of services including film production and box office details, as well as a company directory. Most information contained in the IMDb database proper continues to come from volunteer researchers.

As an additional incentive for users, as of 2003, if users are identified as being one of "the top 100 contributors" in terms of amounts of hard data submitted, they receive complimentary free access to IMDbPro for the following calendar year; for 2006 this was increased to the top 150 contributors, and for 2007 to the top 175. This incentive however is for overall contribution—not contribution on a nation by nation basis.[not in citation given] In 2008 IMDb launched their first official foreign language version with the German IMDb.de. Additionally in 2008 IMDb acquired two other companies. Withoutabox and Box Office Mojo.