Had the birth been successful, the calf would have been the first to be born at the park and only the 12th Pacific walrus to be born in a U.S. zoo, park officials said.
Uquq, the park's 16-year-old walrus, was in labor for more than 40 hours before the stillborn calf was delivered.
"The staff is extremely upset but attending to the welfare of Uquq at this time," Michael Muraco, the park's animal care director, said in a statement.
"We have always known that the survival rate of walruses in zoos and aquariums was only 50 percent and actually less in the wild -- but despite the odds, we felt that all the dynamics were in place ... The odds this time were just not in our favor," he said.
Park officials announced Uquq's pregnancy in April and officials said the pregnancy alone was a significant step for captive reproductive efforts for the species.
The park's marine mammal team, with outside marine mammal reproductive physiologist Holley Muraco, made important discoveries during the pregnancy as to why walruses traditionally have not bred well in a captive environment, park officials said.
"We've learned so much from this pregnancy," Muraco said in a statement. "While there is obvious disappointment and sorrow ... we can apply what we've learned to future walrus breeding opportunities and share that knowledge with other facilities."