Assetz has advanced total facilities of £53.6m in Northern Ireland.
Whitfield was previously with Wellesley and Co-Operative Bank.
The brokerage has moved to larger offices in London and Manchester to accommodate more staff.
This comes at a time when Prime Minister Boris Johnson has finally outlined his “final” negotiating offer for Brexit.
Graham Ritchie joins from Aldermore Bank.
Houses and flats offer the best investments in the North, according to developers.
The lender provides first and second charge short-term property loans.
The properties include converting a former police station into offices.
This is for advisers to refer complex cases such as buy-to-let or bridging.
At Atom Bank, Harris was responsible for creating and launching the bank’s retail mortgages proposition.