They were joined by Megan Fox who showed off her killer curves in a burgundy jersey dress. Jason Segel, Paul Rudd, Leslie Mann and Heather Locklear were also in attendance.
This Is 40 tells the story of a jaded couple who are determined to keep their marriage alive. O'Dowd says the highlight of filming was fighting over Transformers star Megan Fox.
"The best thing was that myself and Jason got to kind of have a whole sequence where we got to fight over Megan Fox which was great."
And while he only married Dawn in August, Chris cheekily admitted Beyonce could tempt him to stray, joking: "Beyonce is the most amazing woman in the world. Waaay before Dawn."
The IT Crowd star said being married was akin to surviving a natural disaster, jesting: "Getting married is like going through an earthquake and we're the survivors. A really sexy earthquake."
They headed to LA for their honeymoon last week but presenter Dawn, who's changed her name on Twitter to Dawn O'Dowd, wrote: "The weather in LA is glorious but nowhere sells swimwear coz it's winter. I am bikiniless."
But it wasn't all good news for Chris as his hit comedy series Moone Boy failed to pick up any gongs at the British Comedy Awards last night.
Chris tweeted saying it was a shame given that child actor David Rawle had come so far "since we found him on the streets of Calcutta."