The prophet Yirmiyahu was one of the three "major prophets" of the Bible, the other two being Yeshayahu (Isaiah) and Yechezkel (Ezekiel). They are "major" because their Books are large, as opposed to the "minor" prophets, whose Books are small. (The "minor" prophets' books are so small that they are combined into a single volume, but we'll come to that in due time.)
Yirmiyahu spent his career as a prophet warning the people to get off the path of destruction they were on. (They didn't listen.) He lived a particularly harsh life, including derision. imprisonment, and being tossed in a pit and left to die. (He was rescued.) The Book ends with the invasion of Jerusalem by the Babylonians and the destruction of the Temple. Yes, there are some uplifting Messianic prophecies in the Book, but for the most part it lacks the consolation found in Isaiah.
Yirmiyahu prophesied during the reigns of kings Yoshiyahu, Yehoachaz, Yehoyakim, Yehoyachin and Tzidkiyahu; his career lasted forty years. He was the teacher of the prophet Baruch and a contemporary of the prophetess Chulda.
Aside from the Book that bears his name, Yirmiyahu also wrote Melachim (Kings) and Eicha (Lamentations). Like the Book of Jeremiah, Melachim ends with the siege of Jerusalem and the Temple. Eicha, of course, is the mourning after Jerusalem was destroyed and is the book read on Tisha B'Av, the day that commemorates the destruction of the Temple.