Terry has been a more prominent figure in Mourinho's Chelsea line-up this season after a number of troubled seasons that culminated in the centre-back struggling to hold his place in the team when Rafael Benitez was in charge last season.
The former England international has been revived following Mourinho's return to Stamford Bridge for a second spell as manager and will captain the Blues on Saturday for the visit of a Cardiff side anxious to focus their efforts on the pitch following a week of off-field upheaval.
And Mourinho is confident Terry has moved on from the succession of problems on and off the pitch that included the loss of the England captaincy and the FA ban for directing racial abuse at QPR's Anton Ferdinand.
"He's recovering his self-esteem," Mourinho said. "In the last few years he was not playing a lot, he had problems on the pitch, he had problems outside the pitch, he had suspensions for different reasons, he had injuries, he had managers who didn't trust him enough.
"And it looked like, at a certain moment, his career was going in the wrong direction.
"Even I was questioning, from far away, what was happening to this guy: physical problems, psychological problems, what is going on? I'm happy he's proving he's still a top player.
"He plays in a position where age doesn't make a huge difference. It's a position where players rely more on positioning, on reading the game, and being in the right place at the right time. Experience helps.
"You go to many top clubs and central defenders are 30 to 34. John is proving his quality.
"With what he did at Chelsea in the last decade, I think he deserves to be back on track."
Chelsea have still to find a consistent run of form following Mourinho's return, although the victory at Norwich before the international break ensured they head into the latest round of matches in third place, just two points behind leaders Arsenal.
And keeper Petr Cech believes the Blues can challenge on all fronts this season.
"We haven't won the Premier League for three years in a row, so I think it would be great to get that back," he said.
"We know how sweet it is to win the European Cup too, so if we could go far in that and really challenge for the title then that would be great."
Cardiff have had a testing week marked by the decision of owner Vincent Tan to replace Iain Moody, the head of recruitment and a close ally of manager Malky Mackay, with the 23-year-old Alisher Apsalyamov.
After several days of speculation surrounding Mackay's future, a club statement confirmed the manager would retain the final say in transfer business.
But the friction has tarnished the start of the promoted club's campaign.
Mackay will undoubtedly work hard to ensure his players' focus remains on the pitch where Craig Bellamy will start after drawing a line under his international career after collecting his 78th cap for Wales in midweek.
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