Trịnh Cối was born in 1584 at Sáo Sơn village, Vĩnh Hùng commune, Vĩnh Lộc district, Thanh Hoa town (now Thanh Hóa province). He was the eldest son of duke Trịnh Kiểm and had a title Marquis Tuấn Đức (俊德侯).

February 1570, Trịnh Kiểm has died, so emperor Lê Anh Tông gave Trịnh Cối the authority with new title Duke Đạt Nghĩa (義達公). However, some officials and generals didn't comply with Trịnh Cối, so they supported his younger brother Trịnh Tùng. April 1570, officials Lê Cập Đệ, Trịnh Vĩnh Thiệu, Trịnh Bách, Phan Công Tích with their inferiors went to Trịnh Tùng's house and advice him to proceed a coup d'état. At first Trịnh Tùng pretened refusing for the surveying, then he agreed completely.

After when Northern dynasty hearded of the news about a confusion in Thanh Hoa, emperor Mạc Mục Tông has assigned prince Mạc Kính Điển in the lead 100,000 soldiers with 700 warships to attack Southern dynasty. August 1570, all of Thanh Hoa produced a stir.