Barkov is coming off a career-high 96-point season. He also finished second among NHL forwards in ice time while being penalized for just eight minutes. He's been a finalist for the award twice but hasn't won.
O'Reilly, who's also been nominated for the Selke Trophy, will be seeking his second Lady Byng after winning in 2013-14 with the Colorado Avalanche. He racked up a career-high 77 points this season while totaling just 12 penalty minutes.
Monahan, a first-time nominee, is also fresh off the best regular season of his career, establishing new highs in goals (34) and assists (48).