Because of the impact of the COVID-19 pandemic on the restaurant industry in the United States, many Denny's had to close for the first time and may now have limited hours of operation.

[5] Denny's was founded by Harold Butler and Richard Jezak in 1953, who opened Danny's Donuts in Lakewood, California, in 1954.

During the 1950s, Los Angeles architects Armet & Davis created a new prototype building with a boomerang-shaped roof that became a model for stores built nationwide.

The diner concept was created by Ron, Marcia, Marc, and Todd York, the principals of Denny's Franchisee SWFRI, Inc.

[15][16] In July 2012, Denny's announced it had signed an agreement with a franchisee to open 50 restaurants in southern China over 15 years, beginning in 2013.

[22] In November 2017, it was announced that Denny's was to open its first UK restaurant in Swansea in December 2017 as part of Parc Tawe's 15 million redevelopment scheme, occupying a 4,000 sq ft unit.

With the company owning and operating 66 with the remaining 1,582 under a franchising model; 1,445 of Denny's 1,602 restaurants are located in the United States (including the District of Columbia), 84 in Canada, 15 in Mexico, 15 in Puerto Rico, 12 in Philippines, 7 in New Zealand, 6 in Honduras, 5 in the UAE, 2 in Guatemala, 3 in Costa Rica, 2 in Guam, 3 in El Salvador, 1 in Indonesia, 1 in Curaçao and 1 in the United Kingdom.

In October 2004, Dateline NBC aired a segment titled "Dirty Dining", in which the ten most popular family and casual dining chains in the United States were examined: Applebee's, Bob Evans, Chili's, Denny's, IHOP, Outback Steakhouse, Red Lobster, Ruby Tuesday, TGI Friday's, and Waffle House.

Denny's attributes this relative success to its adherence to the principles of Hazard Analysis and Critical Control Points.

In 2024, the Humane Society of the United States filed a shareholder proposal requesting that the company reinstate its deadline to eliminate gestation crates from its supply chain.

[36] A 1993 incident occurred when six black United States Secret Service agents visited a Denny's restaurant in Annapolis, Maryland.

The $54.4 million settlement was the largest under federal public accommodations laws established thirty years earlier.

[41] In 1995, a black Denny's customer in Sacramento, California, was told that he and his friends had to pay upfront at the counter upon ordering their meals.

"[49] In 2014, a Denny's location in Deming, New Mexico, was subjected to a discrimination claim by an LGBT group, alleging that wait staff used homophobic slurs and refused to serve a group of gay, lesbian, and transgender customers who were attending a gay pride celebration.

One year later, Denny's agreed to donate $13,000 to Deming Pride, pay $3,250 to a female customer who was subjected to abusive behavior by wait staff, and retrain its employees about discrimination policies.

[50] In 2017, the staff at a Denny's in Vancouver, British Columbia was accused of making an Indigenous woman pay for her meal before it was served.

[51] After the customer left, restaurant staff called police to report the incident, alleging that the patron had a sharp metal object in her pocket.

In addition, several employees claimed there were issues with accounts not being paid, bounced checks, and paychecks not arriving on time.

As a result of the seizure of the eight Denny's locations by the IRS, numerous employees were left without employment and claimed that no advance warning was given regarding the sudden closures.

[54][55] On January 31, 2024, a Denny's location in Oakland, California permanently closed after 54 years of operation, citing the "safety and well-being" of customers and employees.

[56][57] With the advent of delivery services such as Grubhub, DoorDash and Uber Eats, Denny's has begun operating many of their own Ghost kitchens, such as The Meltdown a late-night melt "virtual brand."