Gen Carlos Alberto dos Santos Cruz will lead 20,000 troops, including a new combat force charged with targeting rebels in the east of the country.
This is the most offensive mandate given to any UN peacekeeping force.
Gen Santos Cruz told the BBC his troops would be trained to consider civilians and private property in DR Congo.
“The most critical area is nowadays the eastern part of the country,” he told the BBC’s Newsday programme.
“I am ready to face the most difficult of scenarios. The main objective is to relieve the suffering of the people.”
Gen Santos Cruz will be in charge of a new 2,500-strong brigade tasked with “neutralising and disarming” armed groups which have ravaged eastern DR Congo for the past two decades.
The most recent uprising, by the M23 rebels, began in 2012 and has led some 800,000 people to flee their homes in the mineral-rich region.
Both neighbouring Rwanda and Uganda have denied UN charges that they are supporting the M23.
The UN peacekeeping force in DR Congo, known as Monusco, has been widely criticised as ineffective.
Troops from Tanzania, Malawi, Mozambique and South Africa are likely to form the bulk of the new brigade, which is expected to be deployed by July.
Gen Santos Cruz is a retired former force commander of the Haiti mission, and is credited with dismantling criminal gangs in Haiti in 2007.
UN peacekeeping forces battled for more than a year to regain control of the large Cite Soleil slum in Port au Prince from the gangs.