The Bridesmaids and IT Crowd star confirmed on Twitter that he had become engaged. At the same time, Porter made a similar announcement from her own account.
"I'm so bored of all this happiness and sex. I'm getting married. #engaged," quipped O'Dowd.
"Aw, thanks for all the congrats guys. Feelin the twitter love today. Very happy & lucky boy."
Porter added: "I guess he liked it, coz he put a ring on it #engaged."
Asked for confirmation, Porter said: "At Havelet Bay on boxing day. Very happy x."
Porter, who this year launched a six-part series on the YouTube ChannelFlip station, will feature in the new series of Skins.
O'Dowd recently admitted to doubts over whether a sequel will be made to the summer comedy smash Bridesmaids.
Watch an interview with Chris O'Dowd and Dawn Porter below: