The 19-year-old edge forward has swapped clubs with former Tigers wing Kane Bradley.
Simpkins, a former Rotorua Boy's High School first XV forward, had one game for the Townsville Blackhawks – a Cowboys feeder club – in the under-20s grade last year before the season was aborted due to the Covid-19 pandemic.
He was highly regarded in North Queensland, but Cowboys head of football Micheal Luck said “Tuki had an opportunity to take up a long-term deal with another club, and we wish him all the best’’.
Wests Tigers general manager of football Adam Hartigan said Simpkins was “clearly an exceptional talent’’.
“We’re very excited to see him play his football in a Wests Tigers jersey moving forward,” Hartigan said.
Simpkins, who is 1.92m and 105kg, was first spotted by Cowboys scouts at the New Zealand 15s rugby league tournament in Rotorua in 2016.
He became a New Zealand Secondary Schools rugby league representative and played for the New Zealand Residents team in 2019 before heading to Australia last year.
Luck, a former Warriors forward, praised Simpkins’ stint in Townsville.
“His attitude during a difficult year in 2020 where he and a number of our younger players weren’t able to play any football was first class.’’