Officer Gene Kimpton entered the home in Carrollton, Texas, with his weapon drawn to respond to an unknown emergency.
"It was an unknown emergency. I was expecting a burglary in progress or something like that," Kimpton said.
A young boy guided Kimptom to the bathroom where his mother - who apparently did not realise she was pregnant - was giving birth.
"I get the door open, and she is in the process of giving birth! I put gloves on and helped the baby out," said Kimpton, who has two children of his own.
"It was not what I was expecting in the least bit; but, it was an incredible experience helping a new life into this world," he told CBS 11 News.
Kimpton said the mother did not panic, but she was definitely surprised by the birth.
"She indicated to one of the paramedics that she didn't realise that she was pregnant...At all," he said.
The mother and the baby boy were taken to Baylor Medical Center at Carrollton and are doing well.
