"The petition is dismissed," a bench of Chief Justice G Rohini and Justice Rajiv Sahai Endlaw said.
The court had reserved its verdict on the issue on September 10.
The PIL had been filed by advocate Mithilesh Kumar Pandey, who had challenged the "validity of post-poll alliances among political parties" on the ground that the same was a "breach of the promises made by them during the election campaigns".
"We can't have elections at the drop of a hat," the ASG had said.
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He had also said, "Promises in poll manifestos can only be followed to the extent it is possible", adding that in future, "we may be able to have electoral reforms of this nature when our democracy is more mature".
His PIL had sought a direction "declaring as unconstitutional the practice of post-poll alliances among parties which contested elections against each other".
"Issue directions preventing political parties from violating their own manifestos when such parties enter into post-poll electoral alliances in order to form a government," the petition had stated.
It had also stated that the competent authority be directed to "take steps to make manifesto a legally-binding document".