As a youth, Janus played in his native Slovakia, within the junior program of HC Slovan Bratislava. After his selection to the Lightning in the 2009 NHL Entry Draft, Janus opted to continue his development in North America, playing major junior hockey with the Erie Otters of the Ontario Hockey League (OHL). On December 31, 2009, the Tampa Bay Lightning signed Janus to a three-year, entry-level contract.[1]
Janus claimed the Calder Cup, as the backup with the Admirals in the 2011–12 season, but upon being unable to earn an NHL recall through the duration of his rookie contract with the Lightning he opted to return as a restricted free agent to his original club, HC Slovan Bratislava of the Kontinental Hockey League (KHL) on September 8, 2012.[2]