Tsengwa, who has more than 18 years of executive management and board experience, including the position of general manager of Kumba Iron Ore, will officially take over the reins once Mgojo reaches the retirement age of 63.
"The transition period will ensure a smooth and phased handover of duties and responsibilities," the company said.
Mgojo, who has worked at Exxaro since its inception in 2006, was appointed CEO designate in 2015 before taking the helm in 2016.
For its financial year ending in December, the miner declared a bumper final dividend of 12.43 rand ($0.85) per share, up 6.77 rand from the previous year, and a special dividend of 5.43 rand per share.
Shares in Exxaro were 2% higher by 0800 GMT.
Exxaro, which mines coal, holds stakes in zinc and iron ore mines and operates two wind farms, reported a 2% dip in headline earnings per share for 2020 to 29.55 rand due to one-off costs.
However, revenue rose 12% to 28.9 billion rand and core earnings before interest, taxes, depreciation, and amortisation jumped 25% to 7.291 billion rand.
Coal output increased by 4% to 47.4 million tonnes, driven by higher production at its Grootegeluk mine and the ramp-up of its Belfast mine which offset pandemic-related disruptions at its Leeuwpan and Exxaro Coal Central (ECC) operations.
Exxaro said it was close to finalising the disposal of its ECC mine as part of a strategic review, with an announcement expected in the first half of 2021.
($1 = 14.6709 rand)
(Reporting by Tanisha Heiberg; Editing by Christopher Cushing, Subhranshu Sahu and David Clarke)