The 23-year-old joined the Storks from Hamburg last summer. After a quiet start, he became gradually more involved, especially after the restart, and finished with three goals and one assist from 20 games.
His initial deal had been due to run until next summer, but he is now committed to the club for a further two years.
Sporting director Uwe Stöver said Porath had shown “a great development in the past season,” and the club had been keen to “continue to rely on his football skills, attitude and development potential in the future.”
“I feel very comfortable here in Kiel,” says Porath himself after signing the new contract, which he describes as “a sign of appreciation and trust” from the club in him.
Porath is due to return to training with the rest of his teammates next week.