Marlborough covers an extensive area ranging from the drowned valleys of the Marlborough Sounds in the north, through to the high country of Molesworth. A number of fault lines running through the region form valleys through which several major rivers flow, and are divided by a number of mountain ranges, with over 50 percent of Marlborough steep hill or mountain country.The largest flat area is the Wairau plain. Climate varies considerably from mild and humid in areas such as the Marlborough Sounds through to semi-arid in parts of the east coast and the Awatere Valley. Temperature also varies considerably with some northern coastal areas being virtually frost free, while in the interior, areas such as Molesworth experience frosts almost two thirds of the year.
Natural vegetation ranges from temporate forest mainly in the north to grasslands and scrub in drier areas. A few wetland areas of flax swamp and coastal salt marsh also exist. A number of endangered species are found only in the Marlborough region. Human activity has transformed much of the land, with viticulture, forestry and pastoral farming being major activities.