The Blues skipper was facing up to an uncertain future at Stamford Bridge after being shunted into the shadows by interim coach Rafa Benitez.
The end of the 2012/13 campaign was difficult for Terry and a number of Chelsea's more senior stars, with time seemingly called on their glittering careers at the club.
A change in the dugout has, however, brought about a reversal in fortune, with the vast experience of the likes of Terry and Frank Lampard embraced by Mourinho in his second spell in charge.
Terry claims the Portuguese tactician helped to lift him out of the doldrums and get his game back on track, with renewed belief allowing him to return to top form and become only the fourth man in Chelsea's history to rack up 600 appearances for the club.
He said in the Chelsea FC magazine: "The manager was straight with me from his first day back. He told me, 'Nothing has changed. You can still work and play at the top'.
"That's what I needed to hear at that time and that's exactly what I got from him.
"Jose showed faith in me and to get an arm around your shoulders is something everyone needs from time to time, even if you're one of the more experienced players.
"He made me feel 10 feet tall and it made me want to work even harder for the man in charge."
Mourinho has helped to guide Chelsea to within two points of table-topping Arsenal in the Premier League title race, with Terry admitting that addressing issues away from home has helped to keep the Blues in contention for a first top-flight crown since 2009/10.
He added: "We said we have to improve on that, which we have done.
"The manager got his point across in the way he wants us to play and set up away from home, which naturally took a bit of time, and I think you have to give credit to the sides we have played."