The Portuguese succeeded Louis van Gaal in May 2016 and won the EFL Cup to become the first manager in Red Devils history to win a major trophy in his debut season at the club.
United then won the Europa League to take his first-season tally to three, including August's Community Shield victory.
This term, Mourinho will go up against former club Chelsea in May's FA Cup final to potentially take his United trophy haul to four, as well as improving on last season's sixth-placed finish in the Premier League.
"I knew the club I was coming to," Mourinho told Sky Sports News. "I know that one thing is to go to a club that is prepared to win and you just need to arrive and give the last touches, to give your personal quality, personal knowledge and the team, and the club, is ready just for the last click.
"I knew that was not the case [at United]. The owners knew that. The CEO, he knew that. So when the question was, in this period of my career, am I ready for this kind of job? Yes, I am ready because my career was about new things all the time.
"I was always very Portuguese in the sense that I'm always ready to discover and try new things, always ready to change country, to change club, to change culture, to change everything in the search of new things.
"I did all of that. So when I came in this period to Manchester United I was ready for this and I knew it was not to come and have simultaneous success. But, in spite of it, three trophies, three finals, probably a third or fourth in worst case scenario. Not bad."
Mourinho will go up against old rival Arsene Wenger when United host Arsenal in the league on Sunday.