It was in heard in court that the 42-year-old had been twice the legal drink drive limit when the incident happened.
In a letter read out in court, McPartlin said he is "ashamed and mortified" and "accepts full culpability".
The TV host appeared in court this morning..
Standing in the dock, Ant spoke to confirm his name, date of birth, address and nationality before pleading guilty to a single charge of drink-driving.
The prosecution said that Mr McPartlin had apologised to police for his actions and admitted that he has a problem with alcohol and "emotional issues".
Outside court there were more apologies from McPartlin in a prepared statement and then a hasty exit into a waiting people carrier as shouted questions, not unexpectedly, went unanswered.
After canceling an episode of "Saturday Night Takeaway" following McPartlin's arrest, ITV resumed the series for its final two installments - including a finale filmed at Universal Orlando in Florida - with McPartlin's co-host, Declan Donnelly, presenting solo for the first time.
The court heard that Ant had 75mg of alcohol in 100 millilitres of breath - twice the legal limit.
He told the judge the incident was down to "a brief relapse unbeknownst to his passenger".
Prosecutor Katie Sinnett-Jones said his black Mini hit two other cars after losing control as he drove around a sharp bend at "considerable speed".
McPartlin's vehicle was no longer driveable as a result of the damage sustained.
A witness statement from one of the other drivers involved said that Mr McPartlin's mini rounded a corner "like a rocket". He added that his court appearance was a "turning point" for him.
Of the accident, the Metropolitan Police said one of the passengers of the cars was a child, The Guardian reported.
McPartlin was also told to pay £255 in costs.
'Anthony McPartlin is sorry and is doing everything he can to ensure this never happens again, ' Mr Walker said.
According to BBC News, the star's statement to the court acknowledged he had let himself and many others down.
At the time a statement from McPartlin's publicist added: "Ant has made a decision to go back into treatment and step down from his current TV commitments".