In 1649 the Dutch reported that the young king Le Duy Huu and his uncle had allegedly poisoned Trịnh Tạc.

The situation became so critical that in the autumn of that year, Trịnh Tạc and reinforcements arrived at the battlefield, managed and drove the Nguyễn back to the Gianh River.

In late 1660 Trịnh Tạc planned for an extensive military preparation against the Nguyễn regime in the south and to fend off a potential Qing offensive, which ultimately had little success.

In 1667 Trịnh Tạc's army moved north and attacked the Mạc remnants in Cao Bang, who were formerly under Ming protection.

[5][8] During the Vinh Tho era (1658–1662), Trịnh Tạc and his scholars had reestablished and revived the civil bureaucratic government that had been set up by king Le Thanh Tong in the fifteenth century, by resetting population registers, taxation, reconstructing dykes and roads, reopened state-sponsored schools and civil examinations.

In June 1658, the Swiss superior Onuphre Borges was ordered to recall all the Jesuit missionaries in Hanoi to embark for Macao.

He permitted the French to build a factory at Pho Hien in hope that he would receive more European cannons and to counter the Dutch and Portuguese businesses in Tonkin.

[13] Because of his failed campaign in the same year, Trịnh Tạc turned his anger against the Jesuits and expelled Giovanni Filippo Marini in spring 1673.