Jacks joins fellow Englishman Dawid Malan at the Hurricanes but will be available for the entire season. Malan will miss the early part of the tournament due to England's T20 series in South Africa. Colin Ingram has already been announced as Malan's early-season replacement at the Hurricanes.
Lawrence joins Brisbane as a short-term replacement for fellow Englishmen Tom Banton who will be stuck in quarantine for the early part of the tournament.
Jacks, who turns 22 later this month, has shown plenty of promise in the T20 Blast in England as a top-order batsman who can bowl handy offspin. He made three half-centuries in 12 innings in this year's competition, striking at 149.27, and took 13 wickets with an excellent economy rate of 6.46, including a career-best 4 for 15 in the quarter-final against Kent where he took the new ball and knocked over Kent's star-studded top four.
Jacks has some experience playing club cricket in Australia. He spent part of the 2018-19 summer playing with University Cricket Club in Perth where he made a double century and four other half-centuries in 11 matches. He also played alongside Hurricanes fast bowler David Moody and Australia spinner Ashton Agar with University.
Michael Di Venuto is also a key link having coached Jacks at Surrey, and the pair will reunite again at the Hurricanes where Di Venuto is a batting coach.
"I am incredibly excited about joining the Hurricanes," Jacks said. "I've heard from other English players how good the Big Bash is and I'm looking forward to the opportunity. We managed to reach the final of the T20 Blast at home this summer, so I'm looking forward to hopefully going one step further with Hobart.
"I know Diva very well from his time with Surrey, so I'm excited to work with him and head coach Adam Griffith."
Hurricanes coach Adam Griffith was delighted to add Jacks to his squad.
"Will is an exciting young player who is coming off a very successful T20 Blast in the UK," Griffith said. "He gives us great flexibility in our batting group, as he can open the batting, or finish the innings batting in the middle order. His offspin bowling also adds another dimension to his game."
Lawrence, 23, has plenty of experience in Australia. He was the dominant batsman on the England Lions of Australia last summer scoring 493 runs in just six innings at an average of 98.60 with two centuries and two half-centuries. He can also provide some offspin and was part of a title-winning team with Essex in the 2019 T20 Blast.
"The BBL is a bit of a staple diet for us at home during our winter and it will be enormous to be a part of the League out there this summer," Lawrence said. "The Lions tour was a rewarding one for a lot of the squad and we certainly enjoyed the competitive cricket we got."
"We were able to play in some excellent venues during the tour. We didn't get to play at the Gabba but we had a match at Metricon Stadium on the Gold Coast which was great."
"I kept a pretty close eye on Tom Banton and the other English players who were in the BBL and so coming out to join the Heat is going to give me the chance now to challenge myself again in Australian conditions."
Heat coach Darren Lehmann was delighted to add another dynamic playing into the Heat's top six.
"Dan is a really exciting pick-up for us and has a good reputation as a young player who can influence results with his skills and experience," Lehmann said.
"He caught the eye during the Lions tour with the way he adapted so successfully to local conditions and that is something we think will help at the start of the tournament when we are playing in Canberra and at the Gabba and Metricon Stadium."
The Melbourne Stars confirmed West Indian batsman Nicholas Pooran will be joining the Stars for a six-game stint as early-season cover for Jonny Bairstow. Pakistan quick Haris Rauf is unavailable for the Stars this season due to international duty.