The 25-year-old former Manchester City trainee arrives at the Iron to bolster Paul Hurst's options between the sticks following the recall of Jake Eastwood to Sheffield United earlier in the transfer window.
Lawlor spent seven years in total with the Citizens, progressing to the development team in 2015. After loans to Barnet and Bury, interest came in for the Dublin-born shot stopper in January 2017, with Rovers his eventual suitors.
The Republic of Ireland Under-19 and Under-21 international has made a total of 85 appearances for the Yorkshire side, including 70 league starts.
The goalkeeper takes the Number 13 shirt.