His successor as president, Maithripala Sirisena, drives the decision party, yet neglected to keep his adversary remaining as one of its competitors. BBC Sinhala's Azzam Ameen takes a gander at what is going on.
Who's responsible for the decision party?
The move to permit Mr Rajapaksa to remain for the UPFA coalition has enraged a large number of voters and activists who bolstered Mr Sirisena in his stun triumph in January.
Mr Sirisena assumed control over the administration of the overseeing SLFP and the UPFA coalition it heads in the wake of winning the 8 January vote.
In any case, he has now succumbed to weight from his own particular gathering to give Mr Rajapaksa the selection to keep running for decision.
Since getting to be president, Mr Sirisena has attempted to unite his position inside of the gathering which is loaded with legislators still faithful to Mr Rajapaksa who need to take him back to control.
He has declined to name his opponent as the party's prime clerical cheerful, however Rajapaksa followers are certain their man can make a case for the position on the off chance that he and his supporters win by huge edges in the surveys.
Rajapaksa has a sheltered body electorate, isn't that so?
He does - in Hambantota, his energy base in the south. In any case, he's not remaining there this time. The previous president will keep running in Kurunegala, Sri Lanka's third biggest appointive region, in the north-west.
It has a populace of 1.6 million, while Hambantota is a much littler locale with a littler populace.
To assert some authority for the prevalence, Mr Rajapaksa must win votes in extensive numbers. Hambantota area won't give him those numbers. Kurunegala has numerous armed force families as well, which could help him.
Has Sirisena sold out?
Making space for a political rebound by Mr Rajapaksa has angered numerous who voted in favor of Mr Sirisena in January. They have called the move a "selling out" of the command he acquired to thrashing a man numerous saw as progressively despotic.
"He double-crossed us, we never anticipated that him would join Rajapaksa and bring back the degenerate Rajapaksa administration we crushed," common lobbyist Saman Rathnapriya told BBC Sinhala.
"6.2 million individuals voted against Rajapaksa - not for Sirisena as a man. He has wrecked every one of our trusts," an irate Rathnapriya said after talks went for denying Mr Rajapaksa the gathering selection fizzled a week ago.
President Sirisena had guaranteed not to sell out the noiseless transformation of 8 January or to allow the rebuilding of one-family govern in Sri Lanka.
Be that as it may, following a week's quiet, he tended to the country on 14 July, anticipating his opponent would lose in August.
"Mahinda Rajapaksa who was crushed on 8 January will be vanquished once more," President Sirisena said. "I don't have to peruse the stars to realize that, the future can be anticipated in light of history."
He seemed injured by the general population offend he has confronted.
"No other president has been assaulted the way I have in the previous two weeks - they called me a double crosser and a beast. Today you are tasting the products of vote based system," Mr Sirisena told journalists.
Who's going to win the decision?
Mahinda Rajapaksa is still mainstream among the larger part Sinhalese, a considerable lot of whom recall that he was in control when the armed force crushed Tamil separatists to end years of ridiculous common war.
The UNP party, whose pioneer is at present executive, will have a hard battle staring its in the face.
On the off chance that Mr Rajapaksa wins by a huge edge in his region and the UPFA wins the all inclusive vote, the president could be compelled to name him executive.
That would mean an uneasy cohabitation with the man who unseated him.
Be that as it may, others doubt whether Mr Rajapaksa will have the numbers to end up PM and see the decision as a bound endeavor to recapture power.
Thrashing could see him mortified on the resistance seats, playing minimal more than a spoiler part.
A win, be that as it may, could see the alleged noiseless transformation of 8 January arrive at an end.
