The writer, however, said that he does not need any security and is not scared.
Deputy Commissioner of Police (Special Cell) P S Kushwah said Junaid Chaudhary (21) was nabbed on the intervening night of June 7 and 8 from Wazirabad road in northeast Delhi.
The DCP said Chaudhary was planning to target the writer, known for his controversial remarks. Even though Fatah was not in Delhi, the aide was here to carry out a recce, he said.
A 7.65 mm pistol and four live cartridges were seized from him, the police officer said.
Fatah is known for slamming hardliners and strongly opposing terrorism. Chaudhary, who has orthodox beliefs, was enraged with Fatah's remarks and was preparing to kill the writer, sources said.
He had already received Rs 1.5 lakh in the first installment from some sources and had arranged for weapons from western Uttar Pradesh, they added. He had also recruited a few youths to carry out the plan.
Sources claimed that Chaudhary has said that he will not be deterred by the arrest and will continue in his mission after his release.
The 21-year-old is a resident of Bhagirathi Vihar in Gokalpuri area of north-east Delhi. His father is a milkman.
Chaudhary was arrested in June last year along with Roger Robinson, Yunus and Manish with arms and hawala money sent by Shakeel, but was released on bail within four months. They had been planning to kill Hindu Mahasabha chief Swami Chakrapani at that time.
They were also hatching a plan to kill gangster Chhota Rajan, who is lodged in Tihar jail, at the behest of his arch rival and fugitive don Ibrahim's confidant Shakeel.
However, his aides who were arrested that time have gone their separate ways, police said. One of them is lodged in a jail in some other case while the other two have reformed and one of them is currently in Pune.
Chaudhary contacted Shakeel again but after his bail was cancelled he was sent to Tihar. Later, he was again released on bail and once again got in touch with Shakeel.
Chaudhary then started carrying out the gangster's Delhi-based activities.
Mr Fatah is currently in Canada for his health check-ups but he said that he is not scared.
"These goons do not scare me. I will turn 68 in November and even if they succeed in killing me, the Muslim fight against (radical) Islamism will continue by others," he told PTI in an email response.