The section of Commercial Road between North Bridge roundabout and Bruce Motors will close from Wednesday.
It will allow checks to be carried out on the suitability of the road structure for flood defences in the area.
All businesses in the area will still be accessible to members of the public via a signed diversion route.
Scottish Borders Council said a range of options had been considered - including the use of traffic lights - but that could have extended the works to 10 weeks.
Councillor Gordon Edgar said: "The council realises this will be a major inconvenience to some people in the town and beyond but these works are vital to taking the Hawick flood protection scheme forward.
"The project team need to know the current condition of the road structure in order to take forward suitable flood defences for this part of Hawick, which has previously been badly hit by flooding from the nearby River Teviot.
"The project team, SBC roads department and Transport Scotland will monitor the closure throughout its duration to ensure the diversion route is working safely and effectively."
A stretch of the A7 through Hawick is to close for three weeks during part of the town's flood protection works.