Brown, 25, started his career at Keighley, before moving on to Rochdale and then earning a full-time deal with Huddersfield.
During his time with the Giants, he spent time on a dual-registration deal with the Bulldogs, and scored two tries in their 2010 Northern Rail Cup final triumph over Widnes.
He said: “When I was with Huddersfield I was still quite young but I’m a lot more mature now and understand what it takes to be a Super League player. John Kear was great for me at Batley and I’m very grateful to Craig (Sandercock) and Hull KR for giving me this opportunity to come back into the Super League environment.
“Now that I’ve been given the opportunity, it’s up to me to knuckle down, work hard and repay the faith that Craig and the club have shown in me.”
After finding first team opportunities limited at the John Smith’s Stadium, he switched codes with Sale Sharks, but returned to rugby league with Batley for the 2012 season.
His contract at Craven Park has the option of a further year.
Head Coach Craig Sandercock said: “I saw quite a lot of Batley this season and Alex was a stand out for them on the wing. He has good speed and is a powerful runner. Alex has some real potential and I am confident he has the ability to make the step up to Super League.”