The 42-year-old Ant and Dec star pleaded guilty at Wimbledon Magistrates' Court in London this afternoon and was also banned from driving for 20 months.
He was charged after being involved in a collision with two other cars while driving his Mini in Richmond, London, on 18 March.
In a witness statement, the driver of one of the cars said he and his wife "could have died as a result of Mr McPartlin's reckless driving".
McPartlin was more than double the drink drive limit and had 75 microgrammes of alcohol in 100 millilitres of breath - the legal limit is 35 microgrammes per 100 millilitres of breath.
In a letter read out in court, McPartlin said he is "ashamed and mortified" and "accepts full responsibility". He said he let himself "and so many others down".
The presenter added that he realised people in the public eye should provide a positive example to others and that his court appearance was a "turning point" for him.
His barrister Liam Walker said McPartlin has expressed both his "sorrow and regret" and knows the consequences could have been much worse.
Prosecutor Katie Sinnett-Jones told the court the incident happened at around 3.50pm on 18 March on Lower Richmond Road.
She said McPartlin was driving around a "sharp bend and lost control" and then ended up on the wrong side of the road.
He collided with another Mini Cooper car before driving "straight into the front of an oncoming car".
He is currently seeking rehabilitation treatment and has taken time away from television.
The Britain's Got Talent and Saturday Night Takeaway star first entered a rehabilitation centre in June 2017, after developing an addiction to prescription painkillers following a knee operation in 2015.
Co-presenter Declan Donnelly hosted the final two episodes of Saturday Night Takeaway alone and will also host Britain's Got Talent on his own, although Mr McPartlin was seen on the ITV show over the weekend as the talent show aired its pre-recorded audition shows.