The new body will be known as the HSE and has been formed after almost two years of consultation with stakeholders health and safety Minister Lord McKenzie said.
He said the new body would provide greater clarity and transparency while maintaining its public accountability.
However concerns were raised during the consultation process that the new board would not stand up to scrutiny.
After the second round of consultation, completed at the end of last year, Forum of Private Business national chairman Len Collinson said: "We are concerned that regulators are not properly scrutinised or supervised to make sure the British industry remains competitive and flexible."
But Lord McKenzie defended the move and said: "Now is the right time to merge the organisations into one which can provide a platform for further improvements to health and safety at work across Great Britain."
Chair of the new HSE Judith Hackitt said: "The new Health and Safety Executive will strengthen the importance of workplace health and safety in Great Britain. With a single regulatory body we will be able to strengthen the links between strategy and delivery in order to provide the accountability expected of a public body in today's workplace climate."
The merger will not fundamentally change the day-to-day operations of the department.