Winterbottom, who has spent a decade at the non-bank lender, will continue to support advisers and co-ordinate the business development and lending teams.
The position is a newly-created role.
Avanti said: "Julia has spent over 20 years in the mortgage space, including the last ten with Avanti as one of our award-winning BDM's. Julia has a proven track record in the adviser channel and has been relentless in her support of Avanti and our introducers."
"Her focus will be to see Avanti deliver on its goal to be advisers' non-bank of choice."
The appointment comes as Avanti looks to expand its property team, the lender said.
Avanti Finance has added a specialist property lender to its team in Christchurch.
The experienced Andy Eastgate, (pictured), joins the firm on the south island.
Eastgate has broad experience in the banking and finance sector, most recently working for The Co-operative Bank as a senior lending consultant for over three years.
Before working for The Co-operative Bank, Eastgate was a mortgage adviser for nearly two decades.
He has also worked for the ANZ Bank in various roles from teller to business manager, over a 14 year period.
Avanti said: "Andy thoroughly enjoys working with mortgage advisers, building ongoing relationships, and being able to provide financial solutions to meet the needs of their clients."