He was promoted to Thái bảo ("Grand Protector"), and participated in many battles against Nguyễn lords.
Getting the information, Nguyễn Lữ was afraid, and retreated to Biên Hòa, leaving Tham to defend Gia Định.
After receiving the letter, Tham marched to Biên Hòa, with a white flag in front of the army, to justify his wrongful treatment.
The next year, in 1788, Võ Tánh, a general of Đông Sơn army, decided to join Nguyễn lord's side.
He had to surrender to Nguyễn lord, which marked the end of Tây Sơn rule in Gia Định.