His name came into prominence when he as a Brigadier General was accompanying then Chairman of Joint Chiefs of Staff and Chief of Army Staff General Pervez Musharraf on his way back from Sri Lanka on 12 October 1999 when their plane was denied landing on the orders of Nawaz Sharif at Jinnah Terminal, Karachi, brewing a crisis that ultimately led to overthrow of the Government of Premier Nawaz Sharif.

Major General Shafaat Ullah Shah took the place of Taj and became the new Military Secretary to the President.

Taj continued as the DGMI until February 2005, when he was replaced by Major Gen Mian Nadeem Ijaz Ahmed.

On 29 September 2008, The Australian reported that "Washington is understood to be exerting intense pressure on Pakistan to remove ISI boss Nadeem Taj and two of his deputies because of the key agency's alleged "double-dealing" with the militants.

"[5] Taj took over the XXX Corps after the incumbent Lt Gen Waseem Ahmad Ashraf retired from the army on 4 October 2008.