Brandt still had a year to run on his previous contract but, in extending by a further two seasons, Leverkusen have ruled out the prospect of losing one of their prized assets on a free transfer – as was the case for Schalke when Leon Goretzka sealed his switch to Bayern for next season in January.
"I feel totally comfortable and I see something super big growing here," Brandt told his club's official website .
"This has recently been shown to me by the recent contract renewals of Jonathan Tah and Lars Bender.
"The two of them, just like me, are convinced they can achieve something with this team."
Leverkusen's sporting director Rudi Voller praised Brandt for rejecting the chance to join other "top-class European clubs".
"Julian was already an exceptional player when he came to us as a 17-year-old," said the former Germany striker.
"His current level, however, he would have achieved less quickly without the extensive playing time that he has received from us.
"He had to prove himself early and he did a great job. We are very pleased that he has again decided [to sign] for Bayer Leverkusen, despite a variety of other opportunities at top-class European clubs.
"That shows Julian's character, his great ambition and courage."