Vets at a SeaWorld in Texas say the last ever calf to be born at one of the company's parks is in good shape and being monitored closely.
SeaWorlds were hugely popular in the 1960s, but visitor numbers have declined in recent years amidst negative publicity and criticism by animal rights activists upset by the treatment of captive marine mammals.
Vets at the San Antonio park have not yet determined the gender of the calf, but said the baby and its mother Takara are in good shape and being monitored closely.
Takara was already pregnant when the company said last year that it was suspending its captive breeding program and phasing out killer whale shows at its three parks in Orlando, San Diego, and San Antonio.
"This is the last one, and that makes this a particularly big deal," SeaWorld Chief Zoological Officer Chris Dold said.
"It is a bit bittersweet. We love these killer whales."
The calf was born after an 18-month gestation and is estimated to weigh between 136 and 159 kg and measure between 1.8 to 2.1 metres,
SeaWorld's vice-president of veterinary services, Dr Hendrik Nollens, said it will be the last chance for researchers to study orca development in ways that cannot be done in the wild.
Animal rights group People for Ethical Treatment of Animals (PETA) said SeaWorld should move Takara and her calf from their tank to an "ocean sanctuary," an area of sea enclosed by nets.
"There are a lot of people willing to help," said PETA's corporate affairs specialist, Stephanie Shaw.
"There are companies that have stepped forward and offered major donations.
"These types of seaside sanctuaries are very doable."