Tremain, who has been capped four times in ODIs by Australia, will be available for Northamptonshire's first three games of the season, starting with a trip to Canterbury to face Kent later this week. Morris, the Western Australia quick who enjoyed a breakout summer in the Sheffield Shield, will then arrive for three games in May up until the start of the Vitality Blast.
"Playing county cricket has always been a bucket list thing for me, so I'm really excited to play for Northamptonshire and grateful for the opportunity." Tremain said. "It's been a pretty quick turnaround from the end of our season, so I'm glad we could get everything sorted in time to get me on the plane.
"I'm really excited to meet my team-mates and get stuck in for round one."
Both seamers are known to Northamptonshire's other overseas signing, Sam Whiteman, who captained WA to victory in the recent Sheffield Shield final and has arrived in the UK along with Tremain ahead of the Kent game.
Chris Tremain has been a consistent performer in Shield cricket•Getty Images
Northamptonshire head coach, John Sadler, said: "We're really pleased to have Chris joining us for the first few games. He's got a great skillset and we like his approach to the game, Sam [Whiteman] rates him highly as well which is always a good sign to have that respect from your opposition."
Morris is uncapped but received his first call-up to the Test squad during the South Africa series. Considered one of the fastest bowlers in Australia, Morris finished the Shield season with 31 wickets at 19.96.
"I'm really looking forward to getting over to the UK and joining Northamptonshire for a few games." Morris said. "You hear people talk a lot about county cricket so I'm excited for a new experience.
"It'll be great to link up with Sam [Whiteman] too and hopefully help deliver some positive results for the team while I'm there."
Northamptonshire bowling coach, Chris Liddle, added: "It's great that we have Lance with us for a few games. He possesses express pace and has been highly talked about, I'm looking forward to seeing him charging in wearing a Northamptonshire shirt."