The actor and writer was talking as part of a panel session focused on how the marketing and advertising industry can better work with celebrity talent.
Discussing the ad for a Windows-powered HTC smartphone, Corden said: "I did an ad for Microsoft for a phone where I felt like I was dropped in from a list of 20 people, of which I was number seven after six people had said no; but I had a wedding to pay for."
The actor was joined onstage by talent agent Joanna Scarratt, head of brand partnerships at United Agents; and Zoe Collins, managing executive of Jamie Oliver’s Fresh One Productions.
Expanding on his experience working with Microsoft, Corden added: "It felt like one of the least creative things I’ve been part of - 25 people trying to justify their being in a room and throwing around ideas, none of which was very good.
"I don’t think they succeeded in stopping people buying an iPhone, which I think was the idea."
He also said he was asked to tweet clunky marketing messages such as "Oh man, this HTC Windows phone has far superior qualities to my previous phone".
He did however give an example of a campaign in which he was involved early on in the creative process - a viral for Cadbury. "It was great because it was something I was creatively proud of," he said.
"The reason I say ‘no’ to most ads I’m asked to do is that I feel that if I’m not involved at the start there’s no sense of creatively collaborating."
Corden also questioned the role of social media, and in particular Twitter, in campaigns.
"I’m not 100% convinced by Twitter yet," he admitted. "It looks more powerful than it is. It’s mostly London, predominately left of centre and is still a small percentage of the world.
"It’s essentially people telling you you’re the best thing in the world, or you’re shit. Neither of which is true."
He also laughed off the notion of a Twitter storm: "When you actually talk to real people with actual jobs you see that they have no idea of what you’re talking about. And these are the people that [advertisers] want to find."
The measure of a successful campaign, he said was "if my Auntie Marilyn knows about it".