This is the first time that Wen, who retired earlier this year after a ten-year long tenure, would be surfacing in public. Chinese leaders normally go out of sight after retirement and are rarely seen.
Wen is hosting the lunch at a famous guest house here on October 24, the last day of Singh's visit.
Observers say this is the first time, that a top retired leader would be hosting a visiting foreign leader.
Singh will also be hosted by Premier Li for lunch and in a rare honour, President and Communist Party General Secretary Xi Jinping will host the Prime Minister at a banquet tomorrow.
Observers say these gestures reflect the informal style of China's new leadership headed by President Xi Jinping moving away from the rigid protocol-oriented Communist Party-style of the past.