Watson, 30, replaced fellow countryman Diogo Ferreira who was roped in at the start of the season but did not play a single match for the green and maroon outfit.
“With immense pleasure we wish to inform that Mohun Bagan has recruited Watson Cameron Alexander John in place of Diogo Alexandre Alves Ferreira. Watson is in Australia, he will apply for visa tomorrow (Tuesday) at Melbourne,” a club statement said.
Watson last played for Madura United FC in Indonesia. Before that, he was part of Bengaluru’s squad when they were still in the I-League.
From this year, the former champions jumped ship to join the Indian Super League (ISL) bandwagon.
Mohun Bagan take on Manipur based-side Neroca FC on Tuesday looking for a win after being held to a 1-1 draw by Shillong Lajong in their last engagement. The Sanjoy Sen-coached side have eight points from four matches.