In an internal letter send to General Motor's 48,000 employees, Reilly said he aimed to transform Opel/Vauxhall into a global brand and increase its ability to sell products outside of Europe.
Although Reilly said the manufacturer would not be working with an external agency on the repositioning, he said he was looking to position Opel/Vauxhall as a "leading European manufacturer of high quality, desirable automotive products, based on German engineering".
Reilly revealed that the company had created a working group to define the "Opel/Vauxhall DNA", so that all products and advertising "clearly come from the same home".
The manufacturer will base its marketing activity around a new strapline, ‘Wir leben Autos' ("We live cars"), which was first introduced as the company motto late last year. However, the strapline will not be used in UK-facing Vauxhall campaigns.
In his letter, Reilly implored staff and unions to pull together to create a "positive image of the company". He added: "To help maintain a high image, we should use the long and successful heritage of Opel and Vauxhall and talk about our proven technical expertise."
He also addressed concerns that Opel/Vauxhall should be allowed more autonomy from General Motors, following the failed sale of the business to Canadian parts manufacturer Magna.
Reily said: "We should also not forget that we have been, and continue to be, kept alive during this long period of losses by financial support from Detroit.
"Please remember that while we are responsible and accountable for the performance of Opel/Vauxhall, we should also take maximum advantage of being a member of a leading global automotive family.
"We are better for being part of GM and GM is better for having Opel/Vauxhall."
Under a restructure announced earlier this week, Alain Visser will continue to head sales, marketing and aftersales on the Opel/Vauxhall board, while Andy Gilson remains the most senior marketer for the Vauxhall marque.