He also revealed yesterday that he will not take part this year at I'm Celebrity … Get Me Out Of Here! leaving Donnelly, 42, to present him alone for the first time in 15 years.
McPartlin, also 42 years old, has announced that he will take a break from the small screen until 2019, while he is looking for cures for his addiction to alcohol and prescription.
He and Donnelly together decided to pick up the Saturday Night Takeaway of Ant and Dec of next season, but added that it will be back on the screens in 2020.
The star has said that he will not go under Under the jungle with his sidekick to film the ITV show.
He has been on television since March after being arrested for driving under the influence of alcohol.
McPartlin was hit with a fine of £ 86,000 and handed a 20-month driving ban after pleading guilty to the infraction, leaving a four-year-old girl in need of hospital treatment.
It led him to take time from submitting and going to seek treatment for addiction.
He pulled out of the last two episodes of Saturday Night Takeaway and did not present the live shows of Britain's Got Talent quest.
McPartlin added: "My recovery is going very well and to continue, having talked with Dec and ITV, I made the decision to stop the rest of the year.
"I would like to thank both the Dec and the ITV for their continued support and I can not wait to get back to work in the new year."
Donnelly, who would become a father for the first time with his wife Ali, 40, in September, said: "While I am obviously sad at the thought of not having my best friend in Australia this year, I am proud of the work Ant has done privately and I fully support his decision.
"I do not see the time we get together on the screen in 2019."
Donnelly hosted the final episodes of the ITV series Saturday Night Takeaway without McPartlin at the start of this year.
In a statement the duo declared that "they will bring the show instead in 2020, bigger and better than ever".
Donnelly also hosted the live shows of Britain's Got Talent without his television partner, although McPartlin appeared in the pre-recorded hearings.
The duo has joined Britain Got Talent together since 2007.
ITV's director of television, Kevin Lygo, said: "ITV is completely in favor of Ant that takes all the time it needs for its recovery and this mutual decision to suspend Takeaway in 2019."
McPartlin struggled with a two-year addiction to painkillers, which led him to be admitted to rehab last year.
He had injured his knee in 2014 and underwent an unsuccessful operation the following year which led him to be in severe pain.
McPartlin has implored his wife Lisa, 41, to take him to the hospital in June last year after continuing to binge with tramadol, morphine and alcohol while recovering from a second knee operation.
He admitted he had it passed through the hell but he refused to return to their home in the west of London – and instead he moved to a dance school around the corner.
Lisa, a make-up artist from Strictly Come Dancing, originally hoped the couple would be reunited.
But in January McPartlin revealed that he was leaving her.
He has since moved from Chiswick and lives in the New Malden area to be closer to his new love and his former personal assistant Anne-Marie Corbett, 42.