The Pontypridd MP will serve under Mr Corbyn as shadow Northern Ireland secretary.
And in a sign that the left-winger is flexing his muscles, he also stripped Labour's deputy leader Tom Watson of his role as party chairman and gave it to his campaign chief Ian Lavery.
It means the Prime Minister is nearly as unpopular as Mr Corbyn was in November past year, when he scored -35.
Brent MP Dawn Butler, a longtime Corbyn loyalist who resigned over the party's stance on article 50, will return as shadow minister for diverse communities.
In other moves, the newly elected MP for Kirkcaldy and Cowdenbeath, Lesley Laird, becomes shadow Scottish secretary.
Andrew Gwynne, credited with playing a major role in the general election campaign which saw Mr Corbyn's Labour gain 30 seats, has been appointed shadow communities and local government secretary.
His new role was one of four new appointments announced as part of a modest reshuffle - with most existing shadow ministers expected to remain in their posts.
There had been fevered speculation over whether Mr Corbyn would use his soaring popularity after the election to beef up his frontbench.
But a spokesman for Mr Corbyn said the five appointments are the only changes being made to the shadow cabinet.