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Espiner, who has hosted the programme with Susie Ferguson for nearly five years, is to stay on at RNZ in a reporting role, focusing on long form investigative work across all platforms.
He will remain as co-presenter until a replacement is found and the job is to be advertised before Christmas.
Espiner said he was looking forward to working on stories that would "help inform our important national conversations."
"I'm looking forward to moving out of the studio and into the field again with an opportunity to break some big multi-media stories," he said.
"Guyon has mixed his natural tenacity with his passion for journalism to help Morning Report reveal the truth behind stories," RNZ Head of News and Digital Glen Scanlon said.
"The great thing is we'll continue to work with Guyon as he joins our long-form journalism team - you can expect to hear, see and read a lot more high-quality journalism from him in the future."
In a further change to radio presenting roles, Wallace Chapman and Jim Mora will switch jobs.
Chapman will begin hosting The Panel, every weekday, for Monday 14 January, while Mora will move to Sunday Morning from January 27.
RNZ Head of Radio and Music, David Allan, said audience growth over the past 12 months had provided a great platform for new programming to be introduced in 2019.
This woud include a 5am news and current affairs show which would provide a strong lead-in to Morning Report.