The 42-year-old and her co-host Alison Hammond were joined by the cast of the Mamma Mia party, who opened the show with a vibrant performance of ABBA's hit song, 'Dancing Queen', which took place outside of Television Centre in White City, London.
Addressing viewers after the performance, Holly said: "What a start to the show!"
"We are back from our summer break, but it's not just the start of a new season for our show. For many people out there, today is the first at school. Mine went back today.
"It was all good but we all sort of opened the window and said, 'Oh, summer decided to arrive today,'" she added, before telling viewers what was in store for the rest of the programme.
Holly was absent from the programme for two months, having signed off on her annual summer break on 6 July.
During her absence, a rotating roster of hosts stepped in to cover for Holly, including Friday presenters Alison and Dermot O'Leary, as well as Josie Gibson, Craig Doyle, Andi Peters and Rochelle Humes.
While she was away from the programme, Holly enjoyed spending some quality time with her husband, Dan Baldwin, and their three children – Harry, 14, Bell, 12, and Chester, eight.
In August, Holly was pictured soaking up the sun on a beach in the Algarve in Portugal, and found the time to detail her holiday in her weekly Wylde Moon newsletter.
"This week, as I sit here with my family feeling incredibly blessed to have this time together, it's really got me thinking about how many of these family holidays are left," she penned in a recent post.
She went on to share her sad realisation about her children growing up: "My eldest son, Harry, is 14 this year, and I'm sure it won't be long before he'll start wanting some more independence and to go on holiday with his friends instead of his mum and dad!"
She continued: "The days where my kids need me around the clock are long gone and whilst it's a sad way of looking at things, recognising how truly precious and short this time is, has actually helped me to remain totally present."
Holly's return to This Morning comes amid a turbulent period for the show following the departure of Phillip Schofield in May.
The 61-year-old admitted to lying about an affair with a younger, male colleague in a statement released in June, in which he said he was "deeply sorry" for lying about the relationship and that while it was "unwise, but not illegal," it is now over.
Then in August, a number of ITV employees made claims about the toxic working environment on daytime shows including This Morning, with staff members speaking out about facing "bullying, discrimination and harassment".
The allegations were published by MPs on the House of Commons culture select committee, who are looking into the broadcaster's handling of Phillip's exit. Read the full story here.