Deputy Jeremie Nix was on his way home when a woman flagged him down and told him her baby was unresponsive.
Shortly after, the officer was rushing to a Florida hospital with the 3-month-old boy in his arms.
"I'm not waiting on medics ... I'm headed to the emergency room with the baby," he told a dispatcher Wednesday.
Dashcam video released by the Marion County Sheriff's Office shows the deputy making a U-turn at a red light in Ocala, Florida, before pulling on the side of the road to meet baby Kingston and his mother.
Nix quickly took the baby on his arms and put him on the ground, the video shows.
"I just kind of panicked and started crying and I was just like tell me that he is breathing," the boy's mom, Nechole Crowell, told CNN affiliate WESH.
For several minutes, he performed "several life-saving measures on the child" but didn't see any improvement, the sheriff's office said in a statement.
With no ambulances or medics around, Nix grabbed the boy, got in his patrol car and drove to the Ocala Regional Medical Center.
"I remember praying, thanking God for putting me in the right place, at the right time for the right reason," Nix told reporters Thursday. "This was the most emotional day I've ever had in my career. It was also the scariest and the most rewarding."
Kingston was discharged from the hospital Thursday and is expected to make a full recovery, the sheriff's office said.
"We are tremendously proud of Deputy Nix and we can already see that he and Baby Kingston will have a deep connection that will last a lifetime," the sheriff's office said.