Ainul alias Tarique, who was on life support system, died late last night, hospital Director Arun Kumar Singh said.
"He had splinters, suspectedly hard iron pieces, in his brain and it was not possible to operate on him in that condition," he said.
Ainul was caught while he was running away from a toilet at platform number 10 of Patna railway junction after the first bomb exploded there a few hours before the rally of BJP's prime ministerial candidate Narendra Modi in Gandhi Maidan on October 27.
Some telephone numbers and documents were recovered from the suspect on the basis of which the entire planning by the terrorists was uncovered, police said.
Six people were killed in the serial blasts which left more than 80 injured.