The TV presenter left the ITV show in March after he sparked a record number of complaints by saying he did not believe claims made by Meghan about her mental health in an interview with Oprah Winfrey.
The broadcasting regulator has now ruled that Morgan, 56, was "entitled to say he disbelieved" the royal couple and that "the restriction of such views would be an unwarranted and chilling restriction of freedom of expression".
Morgan tweeted: "I’m delighted OFCOM has endorsed my right to disbelieve the Duke & Duchess of Sussex’s incendiary claims to Oprah Winfrey, many of which have proven to be untrue. This is a resounding victory for free speech and a resounding defeat for Princess Pinocchios. Do I get my job back?"
Watch: Good Morning Britain cleared by Ofcom over Piers Morgan’s comments about Meghan
BREAKING: @Ofcom rejects all complaints against me over Meghan Markle furore that led to my exit from @GMB. Verdict says I was entitled to disbelieve her & Prince Harry & to restrict my right to do so would be a ‘chilling restriction on freedom of expression.’ 👇 pic.twitter.com/m040VOTbKi
— Piers Morgan (@piersmorgan) September 1, 2021
The broadcasting regulator said in a statement: "While we acknowledged that Mr Morgan's questions about the nature of racism had the potential to be highly offensive to some viewers, the conversations about race and racism in this programme provided open debate on the issues raised by the interview.
"We also considered that the programme allowed for an important discussion to be had on the nature and impact of racism.
"ITV had clearly anticipated that racial issues would be discussed at length as part of the coverage of the interview and had taken steps to ensure context could be provided during the discussions.
"Despite strong opinions expressed during the programme, in Ofcom's view any potential offence was justified by the context and the comments and discussions about race and racism were not in breach of rule 2.3 of the code."
Ofcom received 57,793 complaints about Morgan's remarks – the highest in the broadcasting regulator's history.
A spokesperson for the Duke and Duchess of Sussex confirmed that they were among those to lodge a formal complaint.
In the Oprah interview, Meghan said she had approached people in the royal “institution” for help after she had suicidal thoughts, but was turned down.
Morgan said while discussing the interview on GMB: “Who did you go to? What did they say to you? I’m sorry, I don’t believe a word she said, Meghan Markle. I wouldn’t believe it if she read me a weather report."
Later that day ITV released a statement announcing Morgan had "stepped down" from his role as co-host of the breakfast show.
Morgan called his departure from the programme “amicable”, saying: “I had a good chat with ITV and we agreed to disagree.”
He later said: "I believe in freedom of speech, I believe in the right to be allowed to have an opinion. If people want to believe Meghan Markle, that’s entirely their right.
“If I have to fall on my sword for expressing an honestly held opinion about Meghan Markle and that diatribe of bilge that she came out with in that interview, so be it.”
Morgan had co-hosted GMB since 2015.
Watch: Piers Morgan has been nominated for an NTA