If Wikipedia is correct -

"With the Mensheviks and the Bolsheviks clearly diverging, Russian Mensheviks and non-factional social democrats returning from European and American exile in spring-summer of 1917 were forced to take sides. Some re-joined the Mensheviks. Some, like Alexandra Kollontai, joined the Bolsheviks directly. A significant number, including Leon Trotsky and Adolf Joffe, joined the non-factional Petrograd-based anti-war group called Mezhraiontsy, which merged with the Bolsheviks in August 1917. A small but influential group of social democrats associated with Maxim Gorky's newspaper Novaya Zhizn (New Life) refused to join either party."

Accordingly Trotsky was a menshenvik until August 1917.