Shah, a close and controversial aide of Modi, was appointed to the top post in BJP at a meeting of Parliamentary Board where incumbent Rajnath Singh resigned after a tenure of one-and-a-half years.
The former Minister of State for Home in Gujarat and who faces charges in the Sohrabuddin fake encounter case is largely credited for BJP's stunning performance in UP where it got 71 of the 80 Lok Sabha seats.
The meeting was attended among others by Modi, senior leaders L K Advani, Murli Manohar Joshi, M Venkaiah Naidu, Nitin Gadkari and Sushma Swaraj.
Finance Minister Arun Jaitley, who had to table the pre-Budget Economic Survey in Lok Sabha, joined the press conference where the announcement was made by Singh before all these leaders.
"From now and now on, Amit Shah will be the president of the BJP and lead the party. His appointment was asp proved unanimously," he said flanked by Modi and other leaders.
Shortly after the announcement, Modi and Singh offered sweets to Shah while other leaders including Advani, Joshi, Swaraj and Jaitley gave him bouquets.
As reporters started plying him questions, Shah replied "I will speak later" bringing the brief ceremony to a close.