Alton Towers first opened to the public on a regular basis following the opening of Alton Towers railway station. Money raised from railway excursions was paid to the Earl to help maintain the grounds.

In 1924, a group of local estate agents formed Alton Towers Ltd to take ownership of the estate and kept the gardens open as a visitor attraction. The estate was later closed to the public upon its requisition by the military during the Second World War.

In the early 1950s, ownership returned to Alton Towers Ltd, now solely controlled by the Bagshaw family, and the grounds were reopened to the public. From this time, Alton Towers grew as a visitor attraction, with additions including a railway, fairground and, by the 1960s, a boating lake and chairlift. After marrying into the Bagshaw family, property developer John Broome became a director of the family business and began leading its development into a theme park.

Under John Broome's leadership, Alton Towers was opened as a theme park in 1980 with the introduction of a pay-one-price ticket structure and new attractions, including the Corkscrew. The following years saw permanent rides and areas added, including the Log Flume, Talbot Street featuring Around The World in 80 Days, and the Black Hole indoor coaster.

Between 1985–88, further major development saw the opening of a new entrance complex that included the admissions area, themed street with numerous retail and food outlets, a monorail and car parks, as well as the Grand Canyon Rapids and Skyride transport system. Numerous steel roller coasters were also introduced.

In 1990, Broome sold Alton Towers to The Tussauds Group, then a division of Pearson plc, after the park's development of the former Battersea Power Station encountered financial difficulties. The change of park ownership brought another era of major development, involving the opening of many new themed areas and attractions between 1992–97, such as Runaway Mine Train, The Haunted House, Toyland Tours, and Nemesis. The first on-site accommodation, the Alton Towers Hotel, opened in 1996. Tussauds' park development team from 1990 to 2002 included attraction producer John Wardley among others.

The Tussauds Group was sold to venture capital firm Charterhouse in 1998. Oblivion opened that same year. Air (now Galactica) opened in 2002, followed by Spinball Whizzer in 2004. A second hotel and water park, Splash Landing Hotel and Cariba Creek, were opened in 2003.

In 2005, Dubai International Capital (DIC) acquired Tussauds for £800 million. That same year, Rita–Queen of Speed was built in the Ug Land area of the park. Charlie and the Chocolate Factory: The Ride opened in 2006, based on the Roald Dahl book.

In May 2007, The Blackstone Group purchased The Tussauds Group for US$1.9 billion and merged it with its then-subsidiary Merlin Entertainments. Dubai International Capital also gained 20% of Merlin Entertainment.

On 17 July 2007, Alton Towers was sold to private investment firm Prestbury under a sale and leaseback agreement. Merlin continues to operate the site under a renewable 35-year lease. As of 2024, the property is owned by LondonMetric Property.

As of early 2008, the resort changed its name to Alton Towers Resort to better reflect its status as a multi-day destination. At the end of the 2008 season, the Corkscrew closed and its corkscrew track element was placed in the park admissions plaza as a feature in early 2010. TH13TEEN, the first roller coaster to feature a freefall drop track, opened in March 2010 on the former site of the Corkscrew.

In 2020, Alton Towers operated on a shortened season due to the COVID-19 pandemic, operating on a limited capacity from 4 July to 5 November. The resort resumed normal operations on 12 April 2021.

In 2024, Nemesis was revamped as Nemesis Reborn after a year-long refurbishment, along with a revamp of the surrounding Forbidden Valley area. The following year saw the opening of Toxicator in the area, a HUSS suspended topspin, on the former site of Ripsaw. 2025 also saw a cut to entertainment offerings, with the stage on the lawn being removed and a decrease in live actors.

In 2025, Alton Towers announced a new junior roller coaster based on the Bluey (TV series) was being developed for Cbeebies Land, which opened in March 2026, replacing Postman Pat Parcel Post.