The letter to Sonia Gandhi reminded her of the party's 18-point agenda "given to the last chief minister" of Punjab and said that those were "equally relevant today".
Deputy Chief Minister Sukhjinder Randhawa was assigned the portfolios of Home Affairs, Cooperation and Jails, while another Deputy Chief Minister Om Parkash Soni was allotted the portfolios of Health and Family Welfare, Defence Services Welfare and Freedom Fighters.
Sidhu announced his resignation on his Twitter handle in just an hour after Channi announced allocation of portfolios to his Cabinet colleagues.
Charanjit Singh Channi's visit to Delhi assumes significance as Congress leaders Rahul Gandhi and Priyanka Gandhi Vadra had returned to the national capital from Shimla on Wednesday.
Channi, who was the Technical Educational and Industrial Training Minister in the Amarinder Singh, was, for quite some time, a hard critic of the Chief Minister.
A majority of MLAs have proposed his name and the top leaders in Chandigarh are awaiting the green signal from the high command. A meeting is going on at Rahul Gandhi's Delhi residence to decide the next chief minister of Punjab.
Congress veteran Singh resigned as chief minister of Punjab months ahead of the Assembly polls after a bruising power struggle with state party chief Navjot Singh Sidhu.
"The government of Punjab means the security of India, and if Sidhu is made the face of the Congress for chief ministership, I will fight him at every step," Amarinder Singh said.
Sidhu takes over the reins of the party from Sunil Jakhar along with four working presidents -- Sangat Singh Gilzian, Sukhwinder Singh Danny, Pawan Goel and Kuljit Singh Nagra appointed by the party high command to assist him in the run-up to the state Assembly elections next year.