Rees, who was previously head of trading operations at Times Newspapers Ltd, will be replaced by Liam Reynolds, the NGN trading director.
The changes mark the first time in the UK that a newspaper publisher has merged its sales operation to cover both the audience of a broadsheet and red-top tabloid.
The new structure is expected to result in the loss of 100 jobs in a 450-strong sales force, as News International sets about creating agency-focused hubs.
Other changes to the new structure include Naim Halloum, advertising manager at thelondonpaper, taking on the role of head of trading at the daily freesheet, while Sian Roberts, head of magazines at NGN, is to become head of trading for magazines at NI.
All four appointments will report into Dominic Carter, trading director of News International, who was confirmed in the role last week.
Nick Hammond, the Times Media head of solutions, becomes NI head of creative solutions, while Corinne O'Sullivan, Times Media campaign manager, has been appointed NI head of campaign management. James Roles, head of client sales at Times Media, becomes NI head of client development.
The three new appointments will report to the solutions director, a role yet to be filled.
The group has also named four NI key account managers to manage agency relationships. The positions will report to the agency account director, another position that has not yet been filled.
The four new appointments include Terence Cassano, previously NGN head of strategy and planning, Michael Craig, thelondonpaper advertising director, Karin Seymour, TNL group business manager, and Dickie Smith, NGN group business manager.
Paul Hayes, the commercial managing director at News International, said: "This restructured commercial team will provide the experience and focus as we move into our next phase of growth and improved customer service."
Separately, Stuart McDonald takes up the role of head of advertising insight under Claire Myerscough, the business intelligence director, who was confirmed to the position last week. He moves across from the same role in the customer insight team.
Elsewhere, Nicki Blackwell, the advertising systems manager, has been appointed head of systems development, reporting to Patricia Kill, a sales director.
In addition, Alan Butcher, head of advertising publishing, becomes head of advertising operations.