ITV said the show, which saw the reality TV star beat former boxer Tony Bellew and politician Nigel Farage to the crown, was seen by an average of 6.6 million compared to the average of 10.1 million who watched in 2022.
An ITV spokesman said: "I'm A Celebrity is the biggest entertainment show on any channel this year having launched with 10.9 million.
"The series is currently averaging a consolidated 9 million viewers and last night's finale drew a peak overnight audience of 7.6 million (average 6.6 million)."
After his win, announced by presenters Anthony McPartlin and Declan Donnelly, the former Made In Chelsea star leapt into the arms of 41-year-old Bellew.
Speaking to the voters, the 31-year-old said: “I am so grateful, thank you so much, I’ve dreamt of doing this show for years and years and you made this boy’s dream come true.”
His girlfriend, Love Island star Zara McDermott, posted a video to her Instagram which showed jubilant cheers as she and others watched as he was crowned the winner.
Before Thompson’s win was announced, Bellew told Ant and Dec his fellow finalist was like a “fifth son” to him and added: “I definitely think I was put here to be around Sam.”
Thompson, 31, said about the show: “The little moments were the best moments, when Snake Rock camp came back and we had everyone back together, the vibe was so amazing and I don’t think I’ve ever been so happy.”
Earlier in the episode the TV personality ate items including a pig’s vaginaand a camel’s penis when he took part in his final bushtucker trial.
In the eating challenge he also faced a scorpion and finished off the entire critter, including the sting.
Presenter Donnelly joked: “If it stings on the way out, just give the medics a call.”
Speaking this morning, Bellew, 41, praised Thompson and other cast members as “brilliant people” who had helped him get through the show’s trials.
Farage, who came third, also appeared on Good Morning Britain and said his only “agenda” for being on the show was to let the public see the real him and test himself in the trials.
Asked about his reported £1.5 million appearance fee, he said: “Is this the biggest pay check I’ve ever had? Yes, it is and what on earth is wrong with that?”
He also branded PM Rishi Sunak “a lame duck” and said he had “no idea at this moment in time” if he would step back into the political arena but added “never say never”.
Viewers last night saw the 59-year-old reunited with his girlfriend, French politician Laure Ferrari, at the end of the show having earlier gone through his final bushtucker trial when he was locked in the “panic pit”, an underground metal box filled with snakes.
He joked: “Lots of people would like the snake to strangle me, I suppose. Their dream might come true.”
Asked where he was going “in his head”, he said: “I’m thinking about things I’ve done in my life that were worse than this,” adding he was thinking about the plane crash he was in.
And asked if he had dealt with a lot of snakes in his time, he said: “European parliament was stuffed with them, terrible lot.”