Banerjee and the Abdullahs will be attending the politically-significant event in Patna on November 20.
Roy, who is Minister for Parlaimentary Affairs and Food in the Raghubar Das government, was also invited by Kumar for the swearing-in.
"Around 2 pm today Nitish Kumar called Saryu Roy over phone and invited him to attend his swearing-in," a close aide of Roy said in Ranchi. Roy is known to be close to Kumar since the Jaya Prakash Narayan movement days.
Last week, the two leaders had spoken over phone after the Bihar results were announced and Kumar had thanked Banerjee for supporting the grand alliance in Bihar in their fight against BJP.
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The Trinamool Congress chief had also congratulated Kumar over twitter and termed the victory of grand alliance in Bihar as a defeat of "intolerance".
The JD-U leadership had last week extended its support to Banerjee in her fight against BJP and had said that along with AAP and TMC it would fight for strengthening cooperative federalism in the country.
"Just received a call from @NitishKumar ji inviting me to Patna on the 20th for the Oath taking ceremony. I look forward to being there," tweeted Omar in the day.
Earlier, a National Conference spokesman said Farooq Abdullah, the party president and former Chief Minister, has been invited to the swearing-in ceremony of Kumar.
"Nitish Kumar called up the president National Conference personally in the morning and requested his participation in the oath-taking ceremony," the spokesman said in Jammu.