The outlet in Newcastle is the second Glasgow-based Rox has opened in England in quick succession.
The company opened a store in Leeds last month.
Spread across two floors, the Newcastle store is Rox's biggest to date.
Kyron Keogh, managing director of Rox, said: "We have been looking at expansion for some time now and when the opportunity came up in Monument Mall, we jumped at it."
When Rox announced its plans to expand outside Scotland, in June, it predicted that the stores in Leeds and Newcastle would bring in an extra £3 million of sales every year.
Mr Keogh said: "The Leeds store has been performing well since opening last month; it is our first Rox concept store and I'm pleased to say that sales of diamond pieces, in particular, have been very strong.
"Overall the business is performing well and we are trading on par with last year which is great considering current market conditions.
"Average transaction values are up and our strategy of strengthening our luxury watch offering has paid off."