The Northampton hooker was hit with an eight-week ban for biting in March and could only watch as the domestic season drew to a close.
The suspension expired in time for him to join England's Test tour of South Africa and he now has the chance to complete a remarkable change in fortunes by leading the side out this weekend.
With regular captain Chris Robshaw having broken a thumb, head coach Stuart Lancaster has handed the captain's responsibilities for the third Test in Port Elizabeth to the 26-year-old front-rower.
When asked if he could have imagined such a turnaround, Hartley said: "Not as captain, no, but I knew I would be playing again.
"I had two months off so I set goals and targets and I am just happy to be back playing and within the group.
"There was obvious disappointment at picking up the ban but the silver lining to it was I got eight weeks to refocus and train towards something.
"I have been rewarded I suppose, getting back into the Test side and I have enjoyed being back.
"Obviously I was hugely honoured and privileged to be asked to be captain.
"I was flattered the coaches came to me and asked, although I am also disappointed for Chris Robshaw. He has led us very well."
England are hoping to secure a consolation win after defeats in the first two Tests of the three-match series in Durban and Johannesburg but Hartley believes a victory would go deeper than that.
He said: "It is a huge opportunity not only to pick up a huge scalp away from home but to lay down a marker for the autumn Tests coming. Every Test match is a big one."
England's preparations for the clash at the Nelson Mandela Bay Stadium have been disrupted throughout the week by injuries.
Scrum-half Ben Youngs was first forced out with a shoulder problem and then Robshaw had to withdraw.
Prop Alex Corbisiero seemed set to make his return but, after being named in Lancaster's initial side, he has now pulled out after a recurrence of a knee injury.
It has been a frustrating few months for the London Irish loosehead, who missed the end of the domestic season after a bicep operation and then jarred his knee.
He was fit enough to take a place on the bench in the second Test but there will now be no start as Joe Marler retains the number one shirt.
Assistant coach Mike Catt said: "It is obviously a big blow for Alex. He has only had limited opportunities on the tour to show what he is about.
"Unfortunately injuries are part of the game and it has happened to Corbs again.
"It is one of those things you have got to take on the chin and get on with."
Catt himself appears to have made a positive impression on the players since being brought on to the backroom staff by Lancaster for the tour.
Having left London Irish to take up the position, it is a challenge he himself has also enjoyed.
"It has been unbelievable, genuinely amazing," said Port Elizabeth-born Catt, for whom this weekend's game will obviously have added poignancy.
"I have loved every single second of it, coming back to South Africa, and the players have been fantastic.
"The environment Stuart has put in place over the last six months has been unbelievable. Where Stuart is going is in the right direction."
Lancaster is still thought to be looking for another coach and Catt's position will be reviewed at the end of the tour, but he is not thinking about that now.
"I will focus on tomorrow," he said.
"My job is to win a Test match, then we will see where we go."
Catt also agrees that a victory would be psychologically important as the team builds towards the future.
He said: "It would be massive for a group of players who have worked extremely hard.
"A lot of youngsters have come over here for the first time and experienced what true rugby is all about in the heartland of South Africa.
"For us to go into our summer break with a victory against formidable opposition would definitely up the guys' moods a little bit."
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