NRG Energy plans to acquire 5,163MW of energy assets in Maine, California and Texas in the US.
The firm will acquire 3,884MW of Dynegy's assets in California and Maine for $1.36bn from an affiliate of The Blackstone Group.
NRG will also acquire the 1,279MW Cottonwood Generating Station, a gas-fuelled plant in east Texas, from Kelson Limited Partnership for $525m.
The addition of combined-cycle plants in North California lowers the overall carbon intensity of NRG's fleet.
Owning the Cottonwood plant would allow for future contracting opportunities and would enable NRG to provide additional balancing and ancillary services.
NRG Energy president and CEO David Crane said the company has sought for many years to fill the gap in its combined-cycle gas portfolio in its core markets.