This route originally operated to Emory Grove in Reisterstown, but later would be shortened in several steps and gradually replaced by various buses.

Prior this date, Route 5 had used the bus loop of Slade Avenue, Reisterstown Road, and Seven Mile Lane.

The route remained unchanged for more than 20 years, with the exception of a short period of time in which selected trips operated via the Greenhill Apartments.

On June 18, 1984, Route R-4 began operation between the Rogers Avenue Metro Subway Station and Randallstown.

[7] In 1997, MTA proposed to extend Route M-8 about a mile west of Randallstown to the intersection of Deer Park and Winands Roads in Kings Point.

[8] This plan was in response to the many riders who are forced to walk beyond the current loop to reach the residential and commercial development not served by any public bus line.

The original plan for Route M-8 was also to extend the line to the Owings Mills Station, but this was fought due to opposition from residents along McDonogh Road.

Service along Milford Mill Road was previously provided by Route P-6 from 1984 to 1987, which operate from the Reisterstown Plaza Station.

Route M-13 also had a branch to Bellemore Farms via Scotts Level Road that ran every 26 minutes during peak hours.

Other selected M-1 trips during peak hours operated from Milford Mill Station to Bellemore Farms.

The plan to combine routes M-3 and M-8 was first introduced early in 2006 as "Phase II" of the Greater Baltimore Bus Initiative.

When the new combined route started, the layover spot at the intersection of Cumberland and Carey Streets remained.