The appointment of the former general secretary of the Communication Workers Union has been welcomed by the two biggest unions in the health service.
Unison and the Royal College of Nursing described the former work and pensions secretary as 'even-handed' and 'someone we can do business with'.
Royal College of Nursing general secretary Peter Carter said: 'The Royal College of Nursing welcomes Alan Johnson to the post of secretary of state for health and wish him well for his time in office.
'We have gone on the record publicly to praise Mr Johnson's even-handed and open-minded approach which led to a landmark deal to safeguard the final salary pensions of existing NHS nurses. We hope that Mr Johnson will show that same approach on NHS pay.'
The college would speak up when it disagreed with government and 'be vocal in support' when it got things right, Mr Carter said.
'We look forward to a mature working relationship that will be to the benefit of patients first and foremost.'
Unison general secretary David Prentis said: 'We sincerely welcome Alan Johnson to the job, he is someone we can do business with, and it presents staff, patients and government with a clear opportunity to make a fresh start.
'We do hope that the new minister seizes this golden opportunity to listen much more to the real experts in the NHS: staff and patients. NHS leaders need to urgently switch the focus from endless and costly reorganisations and privatisation to more compassionate, patient-centred healthcare.'
Mr Johnson succeeds Patricia Hewitt, who stood down for 'personal reasons', as part of a cabinet reshuffle by prime minister Gordon Brown.
He is a former postman, and became general secretary of the Communication Workers Union in 1993.
After becoming an MP in 1997, in 2004 Mr Johnson entered the cabinet as work and pensions secretary.
In 2005 he was given the post of productivity, energy and industry secretary. The following year he succeeded Ruth Kelly as education secretary.
NHS Confederation chief executive Dr Gill Morgan said: 'Alan Johnson has a strong reputation as a values-driven politician with enormous stamina.
'The employment arm of the NHS Confederation has worked with him recently as part of the review of the NHS pension and we look forward to working with him to keep improving the NHS.'
'Alan Johnson will bring a wealth of experience to the Department of Health in this area from his work with trade unions. It is vitally important that we all work together to turn staff into genuine advocates for the health service.'
She said major issues for Mr Johnson to tackle should be to improve NHS staff morale, deliver local autonomy and measure health outcomes more.
'Patricia Hewitt has overseen a period of great progress in the NHS with falling waiting times, better financial balance and the development of a more open and transparent service,' Dr Morgan added.
'NHS Confederation members have been impressed by her vision and deep understanding of the health service in the numerous meetings we have held with her.
'Being health secretary can, at times, be a thankless task and the courage and resilience that Patricia Hewitt has shown was essential in her success.'
Royal College of Midwives general secretary Dame Karlene Davis commented: 'We are looking to the new secretary of state to put maternity issues at the top of his agenda, halt the decline in the service and deliver the first-class maternity care promised by the government.
'They have an obligation to give women and their families the service they expect and deserve.'
Former health minister Andy Burnham has been appointed chief secretary to the Treasury in the reshuffle.