Strengthening government ranks, which had only a "tenuous" parliamentary majority, by luring opposition members with ministerial positions was also necessary to ensure government stability, said Rajapaksha, seen as a key architect of the military campaign.
Had the government collapsed during the campaign, which ended in May 2009, it would have weakened the war effort, he told an international seminar on Sri Lanka's experience in defeating terrorism organised by the Sri Lanka Army that began Tuesday.
Military officers from 41 countries are taking part in the three-day seminar.
The move drew "a great deal of criticism but was an absolutely necessary step to maintain governmental and political stability," Rajapaksha said.
"Even more important was generating popular support for the war. By 2005 the population had gone from war to peace and back again and there was a lot of cynicism and war weariness among the public at large.
"If the government had focussed only on the war it was entirely possible the people would not have supported the war," Rajapaksha said.
"This was one of the reasons the government invested in welfare even when it could hardly afford to do so because of the war budget.
"For example, fertiliser subsidies were granted when world prices were skyrocketing. This eased a heavy burden on farmers and kept food prices affordable for the general population."
Rajapaksha also said the war was funded and fought at a time when the island was recovering and rebuilding after the devastation caused by the Indian Ocean tsunami just two years before the military campaign began.
"A lot of rebuilding and infrastructure development particularly in power generation and roads was necessary. The government did not ignore these needs."
The government also managed to ward off international pressure to stop the war unlike on previous occasions when foreign intervention stopped a military campaign on the verge of defeating the Tamil Tigers.
"Another key factor determining the success of our operation was management of international pressures by the political leadership," said Rajapaksha, who is the younger brother of Sri Lankan president Mahinda Rajapaksha.
"In 1987 the successful 'Vadamarachchi' operation pushed the (Tigers) to the brink of defeat but could not be sustained because of Indian interference as relations with India were not managed effectively."
In contrast, during the latest campaign President Rajapaksha "went out of his way to brief New Delhi of all developments in Sri Lanka."
"While other countries could mount diplomatic pressure only India could influence the military campaign," Rajapaksha said.The Indian and Sri Lankan governments maintained close ties and clear communications lines at the highest levels that ensured any issues were immediately resolved.