The incident, which unfolded at about 3:15 p.m. local time at Austin-East Magnet School on the east side of Knoxville, marked the latest in a rash of shootings across the United States since mid-March.
Knoxville police said the officer struck by gunfire was expected to survive.
"He is conscious and in good spirits. ... He's going to be okay. I thanked him for putting his life on the line to protect students and staff at the school. He said he'd rather be hurt than anybody else," Mayor Indya Kincannon said.
Investigators did not identify the suspect or slain victim except to say they were both male. It was not yet clear if either was a student at Austin-East Magnet School.
Police established a reunification site for families of the students at the baseball field behind the school.
A mother who had been separated from her daughter was waiting near the school and was relieved to receive a text message from the girl that she was safe.
The Knoxville high school community has been ravaged by gun violence in the last few months, with at least three students at Austin-East having been killed this year.
The school, which had opened its classrooms after pandemic lockdowns, switched to remote learning for a few days in February so that students could grieve the deaths of two 15 year olds and one 16 year old, WBIR-TV News reported.
In other shootings across the United States since mid-March, a man last week opened fire at the Texas cabinet-making plant where he worked, killing one person and wounding six others before he was arrested.
Eight people were slain at Atlanta-area spas, 10 people at a supermarket in Boulder, Colorado, and four people, including a 9-year-old boy, at a real estate office in the Southern California city of Orange.
Source: Reuters