The club officially confirmed the forward's departure from Belle Vue on Monday afternoon.
Horo was in the final year of a two-year deal at Wakefield and was initially thought to have been retiring at the end of the season.
"Trinity can confirm that Justin Horo has left the club by mutual consent," said a short statement on the club's social media.
"We would like to thank Justin for his efforts in the Red, White & Blue and wish him well for the future."
Horo arrived at Wakefield from Catalans Dragons ahead of the 2018 campaign, having made 45 appearances for the French club in a two-year spell from 2016-17.
The 32-year-old made his professional debut for NRL side Parramatta Eels before spending three season at Manly Sea Eagles from 2013 to 2015.
The New Zealand-born forward played 39 times for Trinity, scoring seven tries.