As a child, Leffall had been successful in treating a wounded bird, which sparked his interest for medicine.

Due to a low score on the Medical College Admission Test Leffall had been rejected by Howard.

[3] Leffall earned his medical degree in 1952, attending Howard at a time when Charles Drew was a faculty member there.

[2] After completing training at Memorial Sloan Kettering, while with the United States Army, Leffall spent a year in Munich.

Although he stopped actively practicing medicine in 2013, he maintained his teaching and administrative involvement at the medical school.

[5] In May 2015, Howard held a special grand rounds session to honor Leffall's service to the school.

[3] He served as chairman of the board of directors for the Susan G. Komen Breast Cancer Foundation from 2002 to 2007 and for a few months in 2011 and 2012, as provost at Howard, before he resigned because of increasing responsibilities.

[9] The Society of Surgical Oncology also honored him, appointing Leffall as the first African American president of the organization.