The Sardinians spent only a year in the second tier, something which looked very unlikely when Ranieri took over in December with the team in mid-table.
Eventually finishing fifth in Serie B, Cagliari earned a play-off final against Bari, and after a 1-1 first leg, Leonardo Pavoletti's last-gasp winner earned promotion in the fourth minute of stoppage time.
A former Premier League winner with Leicester, Ranieri was overcome with emotion at full-time and could be heard sobbing thanks to his history with the side.
From 1988 to 1991, he took Cagliari from Serie C to Serie A, a stint which worked as a launchpad for an iconic career in management.
The 71-year-old has had 23 management jobs with 21 different clubs, including Chelsea, Roma, Juventus, Watford and Fulham.
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But soon after achieving the incredible feat, he showed his class as he berated the away end at the Stadio San Nicola for chanting 'Serie B, Serie B' at their defeated rivals.
Expressing his feelings post-match, Ranieri said: "The doubt about coming to Cagliari was about not succeeding, to come back here and not make it would have been a huge defeat.
"Cagliari has allowed me to fly in my career, in Italy and in Europe. There are guys in this team with big hearts. We have so many people behind us who push us.
Asked what he said to the away end, Ranieri replied: "I told them that St. Nicola should have remained silent as we left the stadium.
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"The gesture towards my fans was to prevent them from making fun of opposing fans. I don't understand why you have to cheer against them. You have to cheer for our team.
"Bari were a great rival and we have to shake their hand. I congratulate [Michele] Mignani because he makes his team play very well."
Leading the tributes to the iconic manager was Serbian goalkeeper Boris Radunovic.
"Ranieri is a legend as a coach," he said. "We have been very happy since day one. Everything has changed since he's been here.
"We have become a family. Now I'm going to rest, I'm very tired after 44 games, I'll rest to start again stronger."