The decision was taken on a petition received from Aam Aadmi Party MLA Saurabh Bharadwaj "seeking disqualification of Mishra on grounds of defection," a Delhi Assembly order said.
"Goel has today (on Friday) decided...Mishra, an elected Member of the Legislative Assembly of Delhi, elected from Karawal Nagar, has become subject to disqualification under Paragraph 2 (1) (a) a member of a House belonging to any political party shall be disqualified for being a member of the House, if he has voluntarily given up his membership of such political party of the Tenth Schedule of the Constitution (Disqualification on ground of defection)," the order reads.
It says the disqualification of Mishra takes effect from January 27.
"Consequently, the Karawal Nagar Assembly Constituency seat has fallen vacant," it said.
During the Lok Sabha election, Mishra had campaigned for the BJP and sought votes for Prime Minister Narendra Modi, while the BJP and AAP both were contesting for the seven parliamentary seats in Delhi.
The BJP bagged all the seven seats in the national capital, while the AAP came third.
On July 1, Bhardwaj moved the petition seeking the disqualification Mishra for his association with the BJP.
Bharadwaj, the Greater Kailash MLA, in his petition, said the Karawal Nagar MLA had on January 27 given up the membership of AAP "by way of campaigning for the BJP" at an event hosted by BJP Rajya Sabha MP Vijay Goel.
Delhi Chief Minister Arvind Kejriwal, the leader of the House and also AAP chief, too wrote to the Assembly saying "the party has no objection to Mishra being disqualified from the membership of the Assembly".
Reacting on the matter, Mishra said he does not mind losing his MLA seat for Modi.
"Till now I ran the Campaign 'All seven seats for Modi (in Delhi)', now I will run 'Sixty seats for Modi' for the upcoming assembly polls in Delhi," Mishra tweeted in Hindi.
In a statement, Mishra also said that he was not allowed to present any evidence during the hearing in the Assembly.
"I will go to the court for the decision. I am sure this order will not find any base and it will fall in the court," Mishra added.
On Sunday, Chief Minister Kejriwal had indicated that AAP's Political Affairs Committee member Durgesh Pathak may contest the upcoming Assembly polls from Karawal Nagar, replacing Mishra.
The tenure of the Kejriwal government will come to an end in February, 2020.
( With inputs from IANS )