Phoenix Park perimeter gates will remain closed to traffic.
The OPW says the measure is to ensure that Dubliners can enjoy "a safe, quiet, green space."
Drivers can still access park facilities but it won't serve as a 'rat run'.
Green Party Councillor Michael Pidgeon got around 7,500 signatures on a petition to close the through-road.
That petition was sent into the OPW two weeks ago.
— Michael Pidgeon (@Pidge) June 26, 2020
Pidgeon: We're Not Asking To Ban Cars From The Phoenix Park
Cllr Pidgeon says the park has been a vital escape for residents, particularly during the pandemic:
"They're out walking, I've seen people learning how to ride a bike."
"People have a sense of freedom there."
"While there will still be traffic going down the main road for now - this keeps and improves pedestrian access to other parts of the park."
"It'll make sure that people still have car access to the zoo facilities."
"But it's a quieter, calmer and safer space, more like a park should be."