Patrolman Anthony Reynolds pulled over a car he saw speeding through red lights at about 3:45 p.m. local time on Sunday, Seattle police said in a statement.
As the officer approached the car, the father-to-be jumped out of the driver's side and shouted that his wife was in labor, and pleaded with the officer to let him keep going to a hospital, according to the police statement and audio captured of their interaction.
The officer, after telling him he'd be safer in an ambulance, called for medics.
They were soon joined by three other officers as the couple's baby girl was born.
"The couple's baby was determined to beat medics to the scene," police said, adding that the officers witnessed the "miracle of childbirth."