Spurs locked up a sixth-place finish with a point on Sunday, as Mourinho's side finished the Premier League season with a 1-1 draw against Crystal Palace.
Despite ending the season with a draw, Tottenham did enough to climb all the way to sixth place and seal an automatic spot in the Europa League.
When Mourinho took over following Mauricio Pochettino's dismissal, Spurs sat in 14th place, having earned just 14 points from as many matches in the Premier League.
Harry Kane scored the opening goal for Spurs just 13 minutes on, but a Jeffrey Schlupp goal early in the second half was enough for the two sides to split the points.
And, although Mourinho admitted the performance wasn't quite what the club hoped for, Sunday's result did seal a positive end to what was an overall disappointing campaign.
Under the Portuguese boss, the club completed quite the turnaround, with Mourinho pleased with the progress made so far even if there was a long way to go.
"We, in this group of matches managed to get results and to perform. Not today, it was not the best. But in this period we played well, get results and be solid to put ourselves in the position to get in the Europa League
"From a personal point of view I'm happy because since I arrived we would be fourth which is good with all the problems we had."
Now, with European football secured, Mourinho can look ahead towards continuing to make his mark on the Spurs squad.
The club faces several departures, with Jan Vertonghen and Michel Vorm set to leave, but Mourinho says that he expects to improve the squad this summer.
"When all the players are available we showed in this last period where we belong," he said at his post-match news conference.
"After lockdown we finished third or fourth in the table. That is where we belong. I want to have my team, my players, not a medical room full of players, a pitch full of players.
"We want to keep our very good players and after that improve the squad. Are we going to buy 10 players. No? Are we going to pay £100 million ($125m) for a player? No.
"But let's see. The market is very strange. I don't know if we will start working pre-season with any new players or something that is going to go through the whole period.
"We are going to keep the structure of the team because we have absolutely no interest in selling our best players.
"I enjoy working with [chief scout] Steve Hitchen and we are very connected with [Daniel] Levy and the board.
"We're going to do what is possible and hopefully next season we can give the fans a very good season."