Davis killed Ciaran Morris when he crashed his BMW into the pram carrying the 18-day-old on Brownhills High Street on Easter Sunday last year, before running from the scene.
He denied causing death by dangerous driving, causing death by careless driving and causing death while uninsured, claiming he had a coughing fit behind the wheel.
However, jurors at Wolverhampton Crown Court did not believe the 35-year-old's version of events and convicted him on all three counts.
Davis, from Croxtalls Avenue in Bloxwich, was jailed for six-and-a-half years and banned from driving for seven years and three months after the verdict in April.
His sentence has been reviewed at the Court of Appeal on Wednesday after a request from Attorney General Suella Braverman QC MP, amid calls from regional politicians.
The court found Davis' original sentence to be unduly lenient and added another three-and-a-half years to the sentence.
Ms Braverman, who referred the sentence under the Unduly Lenient Sentence scheme, said: "My thoughts are with the family of Ciaran Morris, who was tragically killed by the criminally dangerous driving of James Davis.
"While no sentence can repair the damage caused by Davis’ actions, I welcome the decision of the Court to impose a sentence that better reflects the dreadful offending that has taken place."
Davis had been travelling at speeds of up to 67mph in a 30mph zone moments before the collision, with the car – according to defence barrister Mr Nicholas Syfret QC – likely to have been doing 29.4mph at the time of the collision, and had been slowing down.
No defects were identified on either vehicle which could have caused or contributed to the collision, and there was no evidence to suggest Davis had been distracted by any activity in the car.
During the trial Davis said he came round from his coughing fit to hear people banging on the car saying "you've killed my baby" and he said his first reaction was to leave the scene as people were saying "get him".
Video footage showed him running from the crash scene. When officer eventually found him at his girlfriend's, their bodycams showed him being told he had killed 18-day-old Ciaran and apologising to his own girlfriend for his actions.
When officers told Davis that Ciaran had died, his legs buckled, he put his hands to his burst into tears.
He can be heard sobbing: "I can't believe it, I've killed a babby. I've killed a babby."
After Ciaran's death blue ribbons adorned Brownhills High Street as people paid tribute to the newborn.