"They will be tremendous assets to the party and the state. We will all work together for the benefit of Odisha," said Patnaik.
Singh said he had already resigned from the primary membership of the Congress after he realised a vested interest group had hijacked the party.
Speculations about Singh joining the BJD had started about ten days ago and after he remained incommunicado for three days added fuel to the fire.
However, five days ago Singh broke his silence and said he had no intention to resign from Congress.
Several other Congress and BJP leaders have recently joined the BJD but the dramatic development of the leader of the Opposition joining the ruling party has sent ripples across the political spectrum.
Reacting to the development, senior Congress leader Sarat Rout alleged Patnaik of poaching from other parties.
"BJD has started all these filthy games misusing its power. Its overcrowded boat will ultimately collapse," Rout said.
BJP spokesperson Suresh Pujari said it shows that the definition of politics has changed radically.
"It is immorality and lack of ethics of the highest order when a person who for the last five years criticised the ruling party as the leader of Opposition and then suddenly decides to join it before the elections. This kind of opportunistic politics is not good for democracy," Pujari said.
The Congress has lost many senior leaders in the past few weeks which has weakened the party's organisational strength ahead of the Lok Sabha as well as the assembly polls in the state.