Not much is known about the early life of Tacitus. Even his first name and father are disputed. It is thought that he was from what is now southern France (Narbonensis). His father may have been an official that served in the region of Belgium and Germany, but that isn't clear. We do know that he was friends with Pliny the Younger. The two exchanged letters but it isn't clear if Tacitus had the same circle of friends or not.
But we do know some things. He started in politics in 81 or 82 and in time moved up the ladder of Roman offices. He served in the provinces from roughly 89 to 93 and may have commanded a legion. This was a rough period, politically but he made it through without losing his life or his wealth.
In 100 he worked with Pliny the Younger to prosecute a proconsul of Africa. The proconsul was accused of corruption and he was found guilty. Young Pliny spoke very highly of his speaking skills.
It's believed that he then took some time off to write the Annals and the Histories. Around 112 or 113 he became governor of the province of Asia. It's believed that he died somewhere between 117 and 130.
Tacitus is generally regarded as the leading Roman historian. He often worked with primary sources, including existing texts of speeches from various Emperors. We're lucky to have the Annals at all. Most of what we have comes from two single copies, one that covered the first six books and the second which covered books 11-16. Even so, there are parts missing. Hopefully, the rest will be discovered in some monastery someday.
It's a shame to think of what immortality of writing has been robbed, not by the judgment of people but by the fault of poor materials.