The TV star took a step back from his work commitments following his arrest for drink-driving in March last year, and his presenting partner Declan Donnelly hosted the live Britain's Got Talent shows alone.
However, the duo are back together in the 13th series of the ITV talent show, which starts on April 6.
Judge Alesha Dixon said of McPartlin's return: "It's been like getting the family back together, it just feels normal.
"We've been working together for so long now that when we're together it just feels right."
McPartlin and Donnelly are celebrating 30 years of working together this year.
Dixon said: "They won at the National TV Awards again this year and I think they are always going to dominate things like that because the longer they are together the more respect people have for them and the more people love them.
"So I can't see that wavering any time soon."
Amanda Holden said it was "so lovely" to have the star back.
"The live shows were not the same without him," said the judge.
Fellow panellist David Walliams said McPartlin's return was an "emotional" one.
"It was lovely to see when they stepped back on the stage in London how excited people were to see them together," said the comedian.
"It was really emotional and I was pleased for them.
"It was just how it always was."
Simon Cowell said he believes the key to the duo's success is that "they are exactly the same guys you see on screen as you see off camera".
The 13th series of the show will see a new crop of hopefuls showing off their talents in a bid to win £250,000 and the opportunity to perform at the Royal Variety Performance.
Among the contestants are "an unusual harpist, a mind-reading dog and one of the most dangerous acts to date".
Donnelly and McPartlin said even after so many series, they were still surprised by some of the auditions.
"We're always shocked by what we see and on series 13 that's no mean feat because you go, 'Well, we've kind of seen it all'," said Donnelly.
"But on more than one occasion this year we've both looked at each other and been like, 'Even after 13 series we've never seen that before'."
McPartlin added: "So this act came on and did synchronised skipping, and we're stood in the wings thinking how we've never seen anything like this before.
"We've had one person do it, but never a huge crew of them doing it to music.
"So it shows there are still people out there who are willing to try new things. It's great. It's been great.
"It's felt a bit like old school Britain's Got Talent where people used to just practice their act in their bedroom and then turn up on the show."
Britain's Got Talent starts on Saturday April 6 at 7.15pm on ITV. It is followed by Britain's Got More Talent at 8.35pm on ITV2.