Brown will bring European and Grand Tour experience to the US Pro Continental team after Svein Tuft retired following the Grand Prix Cycliste de Montreal.
"It's been an amazing six years, but after taking a step back and speaking with my family, we decided Rally UHC Cycling was best suited for the things I still want to achieve in cycling," Brown said in a statement released by Rally UHC.
"I'm really looking forward to getting some opportunities to lead and I'm excited to see what I can do."
Brown came through the USA Cycling development program and Axel Merckx's U23 team before signing with Slipstream's Garmin Sharp team in 2014. His career highlights so far include two days in the polka dot mountains jersey at the 2017 Tour de France, fourth during stage 10 of the 2016 Giro d'Italia and second in the 2013 U23 Liège-Bastogne-Liège.
His last victory came when he won the overall title at the UCI 2.2 Tour de Beauce in 2013 with Merckx's Bontrager team.
"My biggest goal for next year is to win a race," Brown said.
"It's been years since I've raised my hands for a win, and I'm really motivated. I see the team as a fresh start with lots of opportunities, and I feel that I still haven't reached my full potential."
Brown is an especially important addition as the team lost veteran road captain Danny Pate following the 2018 season, and then lost Pate's replacement Tuft this year. Brown brings the benefit of his European and WorldTour experience while still being only 28 years old.
"We definitely expect Nate to take a leadership role," said Rally UHC Performance Director Jonas Carney.
"He's competed in Europe full-time for years, completed six Grand Tours and wore the KOM jersey at the Tour de France. He has a lot of knowledge to share with the rest of our team."
Although Carney praised Brown's experience and ability to take over as a road captain, he also acknowledged the rider still has the physical ability to chase results of his own.
"Nate has spent almost all of his time in the WorldTour working for others," Carney said. "We know he is capable of generating results himself, and our race program will provide him with opportunities in 2020."
Brown is the third and final addition for the Rally UHC men's 2020 roster following the recent signings of Stephen Bassett and Nikolas Zukowsky. With Brandon McNulty joining Team UAE Emirates and retirements of Tuft and Evan Huffman, Rally UHC Cycling returns all 13 remaining riders for the 2020 season.
The 2020 roster will meet up for a team-building camp in Sedona, Arizona, in November before heading to the team's hometown of Minneapolis, Minnesota for the official launch on December 6.
Rally UHC Cycling 2020 men's roster
Adam de Vos