The team announced the decision Wednesday, a day before its season opener against Boston. Eichel becomes the Sabres' 16th full-time captain, and first to wear the "C" since Brian Gionta handled the role from 2014-15 to 2016-17. Buffalo went with alternate captains the past two years.
Eichel, 21, is entering his fourth season since being selected with the No. 2 pick in the 2015 draft. He is also the franchise's highest-paid player with his eight-year, $80 million contract kicking in this season.
Eichel leads the team with 73 goals and 177 points in 209 games during the past three seasons.