Health Secretary Jeremy Hunt has give the go-ahead for a merger between Dorset's South Western Ambulance Foundation Trust (SWASFT) and the Great Western Ambulance Service (GWAS).
One single ambulance Trust will serve the entire South West - from Cornwall to Dorset from February 1.
GWAS Chairman Peter Carr said: "When as a board we decided in August 2011 to identify a partner rather than pursue an application for foundation trust status as an independent trust, our decision was based on the best interests of patients, staff and taxpayers.
"The focus has remained throughout the rigorous process that has resulted in this welcome decision by the Secretary of State.
"I would also like to pay tribute to all GWAS staff who have continued to provide high-quality care to patients during what has undoubtedly been an unsettling time for them personally."
The enlarged Trust will serve over 5.3 million people, with a workforce of around 4,000 people based at more than 120 sites.
Heather Strawbridge, chair of SWASFT added: "I would like to thank staff from both trusts who have worked - and continued to work so hard to make this partnership a reality.
"It has been a pleasure to work with Peter Carr on this project and I thank him for his leadership of GWAS which means our new, expanded SWASFT is starting from a strong operational and clinical position.
"People in the GWAS area now have an opportunity to be part of an NHS foundation trust and I would encourage individuals to join as members and to consider standing as Governors as we are committed to working with our communities to ensure they receive the best ambulance service possible."