The bus route is the successor to the 10 Roland Park, 12 Westport, and 25 Mount Washington streetcar lines.

[4] The initial route of the line was along the Falls Road corridor (current location of the Baltimore Streetcar Museum).

Washington to Key Avenue and Belvedere loop respectively (service to Gwynn Oak was provided by other lines).

In 1982, Route 10, which at the time was operating from Pimlico to Dundalk, was once again split to allow better schedule adherence.

In 1992, in conjunction with the opening of the Central Light Rail Line, Route 27 was truncated to Camden Yards.

Service between Howard Street and Little Italy, and selected trips to Canton were eliminated.

Additionally, selected late night trips were extended to either the Cherry Hill community or to Baltimore Highlands.

Additional modifications in the coming years resulted in all trips being extended to Port Covington via Cherry Hill, and Route 27 in the Cherry Hill area became a supplement to service offered by Route 29.

In 2005, as part of the Greater Baltimore Bus Initiative, a comprehensive overhaul plan for the region's transit system, MTA proposed to discontinue Route 27, and to provide all of its service on other lines.

Because all nine suspects were African American and the victims (except for the bus operator) were white, the incident was originally investigated as a hate crime.

Shortly before 3 pm local time, a Route 27 bus left the Robert Poole Middle School, bound for Port Covington in South Baltimore.

At some point on either West 36th Street or Chestnut Avenue, Sarah Kreager and her boyfriend Troy Ennis boarded.

Kreager and Ennis attempted to find empty seats, but when they located one at the rear of the bus, one of the suspects refused to allow her to sit.

At this point, the suspects attacked Kreager and Ennis, the bus halted after rounding the corner of West 33rd Street and Chestnut Avenue, and the operator called the Maryland Transit Administration Police for assistance.

The suspects were arraigned, charged with aggravated assault and destruction of property, and released to their parents' custody for a hearing schedule for January 8, 2008.

Britny Carter said that Kreager did spit but denies any racial hostility was involved.

Nikita McDaniels was a 15-year-old student at Robert Poole Middle School during the beating and claimed that Sarah Kreager assaulted her by spitting on her and hitting her.

On April 23, 2008, McDaniels was sentenced to serve time in a secure juvenile detention facility.

In his decision, Juvenile Court Judge David Young said it was one of the worst cases he had seen in his 23 years on the bench.

[citation needed] According to the Baltimore Sun, during the trial for five of the accused students, Assistant State's Attorney Dawn Jones accused McDaniels of being the "queen bee" in a "beehive", by taking up two seats on the crowded bus and then harassing Kreager after she boarded and sat down.

[citation needed] On December 10, 2007, Patrick Green and Robert Rothe, both white, were assaulted by a group of young African-American men on the Number 64 Bus in South Baltimore.