Former Manchester United youngster Stewart has found first-team opportunities hard to come by under Steve Bruce at the KC Stadium this season and spent time with Rovers' bitter east Lancashire rivals Burnley earlier in the campaign.
The 21-year-old completed his move to Ewood Park in time to feature in manager Michael Appleton's squad for Saturday's npower Championship clash against Peterborough.
Appleton has been on the lookout for reinforcements on the flanks since a deadline day move for West Brom's Jerome Thomas fell through.
Despite bringing David Bentley back to Blackburn on loan from Tottenham earlier this month, the former Portsmouth and Blackpool boss has seen wide options Josh King, Martin Olsson and Colin Kazim-Richards struck down by injury in recent weeks.
Additionally, Ruben Rochina and Mauro Formica moved to Real Zaragoza and Palermo on loan respectively last month.