He paid a visit to the studio on Thursday and told fans: “So weird to be wearing suit and tie. Been in at @GMB checking the presenter chair and seeing if I can cope with the tech!”
But he insisted: “And no I am NOT the new @piersmorgan.”
Campbell’s stint coincides with Mental Health Awareness Week, which he is championing after his own battles.
His signing is seen as massive coup for the ITV show whose ratings are up year on year and bounced back after Morgan’s departure.
Campbell said: “I am flattered to be asked and delighted that my stint will coincide with Mental Health Awareness Week as Good Morning Britain has always championed good mental health.
“I am also looking forward to getting stuck into the big political and social issues at such an important and difficult time for the country, as well as brushing up my knowledge on some of the subjects that will take me out of my comfort zone.
“In addition, there is an element of finishing unfinished business here... back in the mid 90s I was a regular presenter of the paper reviews on BBC Breakfast and during the week the former Labour Leader John Smith died, I was in discussions with the programme about becoming a presenter. John’s sad death led to me working for Tony Blair and my life and career took a very different course…
“I must admit I am slightly dreading - make that totally dreading - getting out of bed in the middle of the night to get ready to present the show. But I am really looking forward to it.”
Good Morning Britain Editor Neil Thompson said: “We look forward to welcoming Alastair as a guest presenter on the GMB desk this May. He of course has a huge appetite for the world of politics and hard-hitting news but we’ve also seen his vulnerable side, such as his personal struggles with mental ill health.
“A regular panelist on the show who always provokes strong reactions and lively debate, to some he is the architect of spin. To others he is one of the few people in the country able to call things out as they are - something we welcome on GMB.”