Dawson Moves On
The 24 year old, played 97 times for the Shakers, and now moves to London ahead of the new season in a two year deal.
Dawson told Orient's official website: 'It's a dream come true to make the step up to League One and I'm delighted to have agreed to sign for Leyton Orient.
'Everyone wants to play at the highest level that they can and it's great that I've got the chance to step up a division with Orient.
'It was a tough decision to leave Bury - I've got a lot of time for the gaffer Alan Knill and I've got good friends there, but at the same time I can't wait to get started here.
After joining the Stags from Leicester in August 2005, Dawson went on to make 115 starts at Field Mill, scoring on 4 occasions.
He joined Bury on a free transfer in July 2008.