Michael Scott will take over at Norfolk and Suffolk NHS Foundation Trust (NSFT) by the middle of the year.
He is currently head of Norfolk Community Health and Care NHS Trust and replaces Aidan Thomas who resigned last summer.
Mr Scott said he was "committed" to ensuring mental health services were not overlooked.
"I'm going to disappoint people because I don't come with a cheque book," he said.
"Times are tight in the NHS, but what I will commit to do is lobbying hard for resources for mental health, services will be defended and we will work nationally to ensure that mental health services get their fair share of the cake."
Two weeks ago, a Care Quality Commission report said Hellesdon Hospital, run by NSFT, failed to meet expected levels of patient care.
Mr Scott, who has 30 years in the NHS, is chairman of the NHS Confederation's Community Health Services Forum, which helps shapes national policies.
Norfolk Community Health and Care NHS Trust said it will announce its interim leader shortly.
Norfolk and Suffolk's mental health trust has announced its new chief executive.