One person was still missing, Minneapolis Fire Chief John Fruetel said.
One body was found in the rubble more than four hours after the blast at 10:20 a.m. (1420 GMT).
"Of the two missing, we have located one, just one," Fruetel told reporters.
Minnehaha Academy said in a statement that its community was "deeply saddened" by the death of a longtime receptionist. The Christian school also asked for prayers for a second staff member who remained unaccounted for.
The blast occurred while contractors were working on gas equipment inside the Minnehaha Academy, Minneapolis Fire Department Assistant Chief Bryan Tyner said at the scene.
Hennepin County Medical Centre said on Twitter that nine people arrived there for treatment, including one in critical condition.