The country’s stock market fell sharply on news of the appointment, which is seen as reinforcing the hawkish stance of the president towards Tamil rebels.
Like Mr Rajapakse, Mr Wickremanayake is a Sinhala nationalist. The former was premier until winning the presidency.
Mr Wickremanayake has previously advocated a military solution to the conflict with the Tamil Tigers, who have fought a 30-year campaign for a separate homeland for minority Tamils in Sri Lanka’s north and east.
He has also been a strong critic of Norway’s role as negotiator in the deadlocked peace process, and his tough rhetoric against the rebels has been popular within the Sinhalese community.