Johnson, who was born in New York, was the Prime Minister for three years, steering the nation through the Coronavirus pandemic and spearheaded the fastest vaccination rollout in Europea during his tenure.
He has been replaced by Liz Truss, who takes the reins at Number 10 amid soaring energy prices and the cost of living crisis.
In his speech, Mr Johnson compared himself to Cincinnatus, a Roman dictator who returned to leadership, suggesting that he may return to contest the leadership of the party again in the future.
Johnson said: “On the subject of bouncing around in future careers, let me say that I am now like one of those booster rockets that has fulfilled its function.
“I will now be gently re-entering the atmosphere and splashing down invisibly in some remote and obscure corner of the Pacific.
“Like Cincinnatus, I am returning to my plough and I will be offering nothing but the most fervent support.”
His reference to the Roman statesmen has now fuelled speculation that he may return to frontline politics.
The comment in his speech was quickly analysed by many, including well known political journalist, Andrew Neil.
On his official Twitter account, Neil said: “This is not the speech of a departing prime minister who necessarily thinks he’s going away for ever.
“And he’s enough of a classics scholar to know, in comparing himself with Cincinnatus leaving for his farm, that when the call came Cincinnatus returned to Rome.”
Who is Cincinnatus?
According to more traditional accounts, Cincinnatus was born around 519 BC, the last decade of the Roman Kingdom.
Cincinnatus was made a dictator in 458 BC to lead the battle against invasion, before returning to his “plough” (farm) just 15 days after power was initially granted to him.
He became famous for his resistance to hang on to power for too long, and for not meddling in politics.
According to tradition, he then returned to serve a second stint as a leader.
He is now often cited as an example of outstanding leadership, service to the greater good, civic virtue, humility, and modesty.
He has a statue in the Tuileries Gardens in Paris, and the Cincinnato neighbourhood in Anzio, Italy is named in his honour.
What else did Boris Johnson say?
His farewell address lasted just under 10 minutes, where he referenced his dog, Dilyn, Vladimir Putin and some of his achievements over the last three years in power.
He also referred to the cost of living crisis during his farewell speech, saying: “This is a tough time for the economy. This is a tough time for families up and down the country. We can and we will get through it. We will come out stronger on the other side.”