[5] Before merging with Exelon, Constellation Energy Group operated more than 35 power plants in 11 states (mainly Maryland, Pennsylvania, New York, West Virginia, and California).

[6] On September 15, 2005, Constellation Energy announced a joint venture, UniStar Nuclear, with Areva to market the European Pressurized Reactor (EPR) in the United States.

The next day, as the stock fell as low as $13 a share, the company announced it was hiring Morgan Stanley and UBS to advise it on "strategic alternatives" suggesting a buyout.

[12][13] In January 2009, Constellation Energy announced it would sell the majority of its London-based international commodities business to an affiliate of Goldman Sachs for an undisclosed price.

In November 2014, it completed its acquisition of Integrys Energy Services, a competitive retail electricity and natural gas subsidiary serving customers in 22 states.

In September 2016, it completed its acquisition of the retail electricity and natural gas business from ConEdison Solutions, a subsidiary of Consolidated Edison, Inc.

In the purchase, Constellation acquired ConEdison's retail electricity and natural gas customer contracts and associated supply contracts serving approximately 15 TWh of electricity and 1 billion cubic feet per annum (28,000,000 m3/a) of natural gas to more than 560,000 commercial, industrial, public sector and residential customers.

In September 2024 Microsoft entered a contract with the company that will restart the undamaged nuclear reactor at the Three Mile Island plant.

[23] In January 2025, Constellation agreed to acquire the natural gas and geothermal power provider Calpine for $16.4 billion ($26.6bn including debt) in a cash-and-stock deal.

[2] As of 2018[update], Constellation had around 360 megawatts of solar generation assets that are either in operation or under construction across the United States, including Maryland,[25] California, Arizona, New Jersey, and Texas.

The company oversees trading, transport, and storage of physical gas supply, pricing, hedging, and risk management.

Their portfolio includes Proterra, ChargePoint and Aquion Energy[27] Constellation is the United States' leading nuclear power plant operator, with over 19,000 megawatts.

CGS functions as an industry-leading maintenance and technical services organization emphasizing precision and quality, structured to streamline the work execution of the nuclear fleet.