On 25 October 2009 Lydiate was named in the Wales national squad for the November 2009 international series, making his debut as a second-half replacement against Argentina on 21 November 2009. Following the withdrawal of captain Ryan Jones from the Wales squad to face Australia in the final Autumn International, Lydiate made his first test match start at flanker on 28 November 2009. He was named in the Wales squad for the 2010 Six Nations Championship, however did not play a single game. He then broke into the Welsh first XV in the autumn internationals of that year, starting against Australia, New Zealand and Fiji as well as being named in the team to face South Africa before withdrawing with a calf injury. He won the Man of the Match award against the Fijians, where he wore the Number 7 jersey for the first time.