Although he hasn't played since 2015, Montreal felt strongly enough about Manziel to surrender two future first-round picks to Hamilton in the five-player deal.
Manziel, 25, had been serving as a backup in Hamilton, where Jeremiah Masoli is entrenched as the starter after a CFL record nine-straight 300-yard passing performances.
Meanwhile, the Alouettes are 1-4 and rank last in the CFL in points scored and have already tried out three different quarterbacks under center, with none showing much in the way of efficiency.
Alouettes head coach Mike Sherman has known Manziel for several years.
Manziel signed a two-year contract with the Tiger-Cats in May, looking to salvage his football career after a turbulent and unsuccessful stay with the Cleveland Browns, who made him the No. 22 overall draft pick in 2014.
The 2012 Heisman Trophy victor at Texas A&M was 21-of-32 for 168 yards and a touchdown in two CFL exhibition games with Hamilton. "With his great mobility, his athletic abilities and his instinct we believe that he will have a positive impact on our offence". He was released in March 2016 after posting a 2-6 record over two tumultuous campaigns.
Manziel might actually get some playing time as he attempts to make it back to the NFL. They will take on the Ottawa Redblacks next week at Tim Horton's Field, while the Alouettes will play host to the Edmonton Eskimos.