The actor joins the likes of Sir Alex Ferguson and Robbie Williams

Fellow high-profile ambassadors include Sir Roger Moore, Sir Alex Ferguson, Jemima Khan and Ralph Fiennes.

McGregor decided to work with Unicef while undertaking a round-the-world motorcycle trip during which he saw close-up the problems facing children.

He said: "I vowed then and there to devote time and effort to do as much as I could for Unicef once I returned.

"The journey was a short one and I was determined to make working with Unicef not just something that I did on the trip but something I would do for the rest of my life.

"I am so honoured to have been given this opportunity to become an ambassador. It's a new and different venture for me and one that I know will widen my perspective on life.

"I'm in a position to use the recognition from my work to do something really positive for children."

McGregor, who has starred in movie blockbusters including Star Wars and Trainspotting, is father to Clara, aged eight, and two-year-old Esther.