The pair were flagged down by a father whose wife was giving birth in a taxi in west London.
PC Laidler checked the umbilical cord was free and the vital signs were strong while his partner PC Murphy called in paramedics.
The birth took place at 1.30am on in Broadway, Southall and mother, baby and father are all well, police said.
The officers were praised by their superiors who revealed that the officers had been dealing with a murder only hours earlier.
Detective Chief Superintendent Peter Gardner, West Area commander, said: “For a police officer, every call to action is different and the ability to adapt to each situation is essential.
“On the night before the birth of the baby boy, these two officers had been deployed to a homicide, the polar opposite of a birth.
“To have dealt with two incidents of such contrast in just 24 hours has clearly demonstrated their ability to react appropriately no matter what they encounter as they go about their duties. The officers are a credit to the organisation and to London.”