Order of the Phoenix

It is mentioned that Andromeda Black was burned off the tapestry of the Black family tree because she married Ted Tonks, a Muggle (in fact, a Muggle-born wizard). This made Andromeda a blood traitor.

Deathly Hallows

When Harry Potter has to leave the Dursleys' house because the blood protection he received from his mother will end when he becomes of age, it is to Ted Tonks house that he will go first. He crashes on the grounds of the house, and Ted heals his injuries.

When Remus Lupin follows Harry to Grimmauld Place, he is volunteering to travel with Harry, Hermione, and Ron, to give them any help he can. He says that he has left Tonks (which would be Nymphadora) with Ted and Andromeda. Harry sends him back to take care of Dora and their unborn child.

Near the beginning of December, Harry, Hermione, and Ron hear a group of people who are traveling through the countryside, to escape the current Ministry edicts. Ted is among their number, and he passes on some information about the sword of Gryffindor.

Ron, when he returns to the group, brings a small wireless with him. This wireless will occasionally pick up a program called "Potterwatch", a pirate signal that tells the true news of what is going on. The one program they receive, around the end of March, tells that Ted had been killed, along with two other members of the group that had been traveling with him.