This, he said, was his second mistake after supporting VP Singh who led a Janata Dal government supported by the BJP and Left parties from outside.
"I made two mistakes -- by supporting (former Prime Minister) VP Singh and then by supporting Modi," Mr Shourie said, addressing the sixth Khushwant Singh Literary Festival at Kasauli.
Mr Shourie was speaking on "How to recognise rulers for what they are".
"Don't go by what these fellows say now. Go by what they have been saying in the past," he said.
"Actually don't even go by what they are saying, but go by what they have been doing and what they have condoned in other people. So, that is very important for the future."
He said leaders should also be judged by examining their claims "in great detail".
"I think this is one of our great failures, of our newspapers, of people like me who did not examine the claims about the Gujarat model," he said, referring to PM Modi's claims of Gujarat development when he was Chief Minister of the state.
He also castigated the government over its job claims, saying between January and April this year 1.5 million jobs have been lost.
"And they had promised to create 2 crore jobs per year. But four days ago, there were full page ads that they have created five and half crore jobs. What kind of magic is this that so many jobs were created but we can't see it."
He said that in politics the main point to watch for a leader was their character and their adherence to truth.
"If that is not there many other things will also not. Never believe that certain things being said by people close to a person are not being said by the person. Such leaders are ventriloquists," said Mr Shourie.
"Just believe I am talking about (US President) Donald Trump. Any resemblance closer home is your imagination."