Finding a complete English translation of the entire work in a single PDF is difficult, as many translations focus on specific sections. Below are the most reputable English resources available: Muslim Sects and Divisions
Written around 1127–1128 CE, Al-Milal wa al-Nihal is a monumental encyclopedia of the religious and philosophical movements known to the 12th-century Islamic world. Unlike many of his contemporaries, Al-Shahrastani is praised for his relatively objective and non-polemical approach, often presenting the views of various sects without immediate vituperation. The work is traditionally divided into two major sections: al-milal wa al-nihal english pdf
Find Al-Milal wa al-Nihal in Arabic (available on Al-Maktaba al-Shamela or archive.org). Finding a complete English translation of the entire