The unanimous opinion of the scholars of Ahle Sunnah Wal Jama`ah is that Abu Talib died as a non-muslim.

Bukhari and Muslim both narrate from Abu Said Al Khudri that he heard the Messenger of Allah say, when his uncle Abu Talib was mentioned:

“..my Intercession will help him on the Day of resurrection, so that he may be put in a shallow part of hell, with fire reaching to his ankles and causing his brain to boil.” (Bukhari in Kitab Al Riqaq Fath Al Bari Vol 11/417, Muslim in Kitab Al Iman, Bab Shifat an Nabi)

Allah knows best
[Answer provided by: Muhammad Salim Ghisa]