The scheme will reshape one of the world's most well-known shopping areas, as well as Europe's largest high street.
The road will also be narrowed, accommodating a two-way traffic flow with pedestrian priority crossings. These will sit alongside a range of other traffic calming measures designed to encourage slower driving.
Among other features in the concept designs are a number of 'off-street oases' which, according to the practice, will create 'inviting pause points away from the bustle of the street'.
The practice also aims to 'de-clutter' Regent Street and improve the crossing points. Low-energy LED light masts will be used to light the strip.
Gillespies' partner Steve Wardell said: 'From a designer's perspective the chance to transform Oxford Street is a once-in-a-lifetime opportunity and one that is well overdue.
'We really want to seize the opportunity we have been given to make a difference. The designs will improve the experiences of a large number of people and this has been the priority throughout this project.'