Mr Umunna, 32, who was only elected to Parliament in 2010, will take on the role shadowing Liberal Democrat Vince Cable after John Denham stepped down.
The reshuffle comes after party rules were changed at the recent conference so that Mr Miliband could select his own team of MPs rather than only being able to choose from those elected to the shadow cabinet in a ballot.
Mr Umunna, the MP for Streatham, studied at the University of Manchester and University of Burgundy before attending Nottingham Law School. He is seen as a rising star in the party and was formerly shadow minister for small business and enterprise.
He takes on the brief after Mr Miliband’s eye-catching announcement at the party’s annual conference that Labour would cap tuition fees at £6,000 if it were in power now.
It has been reported that Mr Denham, who has agreed to take on a more junior role as Mr Miliband’s Parliamentary Private Secretary, had indicated to the Labour leader that he wanted to leave the role some time ago. He is believed to be planning to step down as an MP at the next election.
However, there has still been some surprise at his decision to stand down given he is one of Labour’s most experienced MPs and received praise from some quarters for his handling of opposition to the government’s university funding reforms.
One rumour circulating at the party’s conference in Liverpool was that there was tension between Mr Denham’s team and the leadership over the way the £6,000 cap policy was announced.