Flanker Harley was awarded the McCrea Financial Services Player of the Year award for his performances last season and will captain the side for the first half of the coming campaign.
Prop Grant meanwhile will pack down with new signing Mike Cusack in the front-row for the Warriors' final warm-up game against Sale Sharks on Friday night.
And Lineen believes the pair will have a big part to play in Glasgow's fortunes this year.
"Rob's a fantastic talent and character who we're delighted to have back with us," he said.
"It's a sign of his ambition and desire to progress in the game that he's disappointed not to be going to the Rugby World Cup, but he's hungry to do well for the Warriors and I've every confidence he'll hit the ground running.
"It's also great to have Ryan Grant back in the team, and with a big scrummaging unit like Mike Cusack on the other side, I like the look of our front row.
"It was always our intention to give as many guys as possible a chance to impress between the Newcastle and Sale games, and that's exactly what we're doing by making a few changes for the Sale game.
"We showed excellent fitness and resilience to push on in the Falcons match and ultimately win it, and I'm looking forward to seeing us build on that at Edgeley Park.
"It's going to be another very worthwhile runout ahead of the RaboDirect PRO12 beginning at Ulster next Friday. There will be no margin for error that night, so we're looking for a slick performance to set us up for Belfast."
Harley will get a taste of the captaincy on Friday night against the Sharks and says he is relishing the opportunity to lead the Warriors into battle.
"I love playing for Glasgow and take a great pride in pulling on that jersey," he said. "The extra responsibility of being captain is something I'll relish, and it's great to be able to call on the support of the core of experienced players that we have at the club even with a good number of guys away with Scotland.
"I've learned a lot from being part of the wider Scotland squad all summer, and I'm looking forward to putting that into practice with Glasgow over the coming weeks and months."
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