It will take over from Care UK in all areas except Staffordshire, where the 24-hour-a-day, seven-day-a-week health phone line will continue to be run by Vocare.
Workers will transfer over to WMAS, which intends to boost staff numbers ready for the busy winter period.
WMAS stepped in to lead on the 111 service in parts of the Midlands for over a year in 2013, but lost the contract when it was put out to tender again.
Taking over the service in November, ambulance bosses say integrating the 999 and 111 services in the West Midlands will lead to 'significant improvements for patient care'.
Call handlers across three sites will be able to deal with both 999 and 111 calls and there will be retraining for all staff, WMAS says.
WMAS chief executive Anthony Marsh said: “We have an outstanding track record in running complex clinical call handling operations.
"This expertise will allow us to bring real improvements to the 111 service for both patients and our staff.
“We will initially deliver the current service over the winter period but will then look to properly integrate the two in 2020.
"Staff currently employed by Care UK will TUPE (Transfer of Undertakings Protection of Employment) to WMAS.
“We will also be looking to significantly increase the number of staff so that there is more resilience over the winter period.
“I firmly believe that this will be positive for both sets of staff for example, providing new opportunities to develop and progress their careers.
“People who need help in an urgent or emergency situation are often anxious and may be unsure how to access NHS services. By integrating 111 and 999, patients can be better directed to the most appropriate care for their needs.
“It won’t matter which number you use, it will be handled by a call handler who will be able to deal with either type. Call 999 only for life threatening conditions.
"Call 111 if it isn’t an immediate emergency or a life-threatening condition; whatever number you ring the ambulance service will manage your call.”
Health commissioners say WMAS will be able to draw on other health resources in the community, which could lead to fewer unnecessary ambulance journeys to A&E.
Rachael Ellis, chief officer for Integrated urgent and emergency care at Sandwell and West Birmingham Clinical Commissioning Group, said: “This is truly a first for the country and will lead to real benefits for patients and staff.
“The new service in development will see fewer patients being sent ambulances and a reduction in the number of patients asked to attend A&E.
"The new model will support more patients being cared for in the most appropriate place for their needs.
“This will also include more patients being provided with care over the phone by a team including GPs; other healthcare staff including advanced nurse practitioners; community mental health teams; pharmacists, dental nurses, paramedics and midwives.
“We would also expect to see more calls diverted to GPs, in and out of hours, urgent treatment centres and rapid response services operated in the community.”
Union bosses say returning the contract to the NHS is good news for patients across Shropshire and the West Midlands.
Unison West Midlands regional organiser Chanel Willis said: “The big winners from the return of the 111 service to the public sector will be patients.
"From November they’ll once again be able to speak with highly trained NHS staff.
“When NHS services are privatised the concern is always that costs will be kept down to drive up profits.
"Unison is pleased that after four years health bosses have finally realised the 111 service is safer in the NHS family.”