William Thomas McKinley was a composer whose career embodied a distinctly American musical eclecticism. Known as Tom to his friends and family, his life and work intertwined with cultural icons as diverse as guitarist Wes Montgomery and American baseball catcher Carlton Fisk. A prolific writer, an inspiring teacher, and a lively raconteur, McKinley's early musical explorations began in his hometown of New Kensington, PA, where he was born into an Irish working-class family with a distant connection to the twenty-fifth president, William McKinley. He displayed a talent for intricate piano improvisations from an early age, starting lessons at six and performing professionally with dance bands by ten, and becoming the youngest member of the American Federation of Musicians in Pittsburgh at age eleven.

Despite gaining recognition as a performer alongside jazz greats like Dexter Gordon and Wes Montgomery, McKinley pursued music composition at Carnegie Tech (now Carnegie-Mellon), studying under Nikolai Lopatnikoff rather than opting for a performance degree. Beginning formal composition studies in 1958, McKinley melded Lopatnikoff’s neoclassical influences with his passion for jazz improvisation and Aaron Copland’s melodic style, shaping the foundation of his early works. His talent was recognized with a summer fellowship at the Tanglewood Institute and a BMI composition award in 1963, and an invitation from Mel Powell to Yale's graduate program in 1965.

At Yale, McKinley shifted towards a modernist language under the influence of the prevailing European serialism at the time, encouraged by Powell and supported by fellow classmates like saxophonist Les Thimmig and clarinetist Richard Stoltzman. His time at Yale yielded commissions, another Tanglewood summer, and a teaching position at SUNY Albany before graduating in 1969. He later secured a tenure-track teaching position at the University of Chicago, however he found limited scope to explore his jazz interests. At the invitation of Gunther Schuller, McKinley joined the faculty of the New England Conservatory of Music in 1973 , teaching in both the Composition department and Jazz Studies department (then known as the department of Afro-American Music). He would go on teach for over two decades at NEC, briefly chairing the jazz department, shaping the curriculum in jazz theory, orchestration, and composition, and mentoring generations of students.

Transitioning away from his dual role as a performer in the early 1980s, McKinley focused intensely on composition, refining his style amidst the changing musical landscape. Embracing both American minimalism and a more direct, neo-tonal, neo-romantic approach, he integrated his love for jazz with classical concert music, marking a pinnacle in his career, earning accolades such as the American Academy of Arts and Letters Music Prize (1983), a Koussevitsky Foundation Commission (1984), and a Guggenheim Fellowship (1985). Notably, he composed several significant works for tenor saxophonist Stan Getz during this period, symbolizing the culmination of his musical journey.

After retiring from full-time teaching, McKinley continued to compose , teach privately, and occasionally perform in the Boston area. In the early 1990s, he founded a recording company, Master Musicians Collective (MMC), providing a platform for recording and distributing music by living composers. Until his passing, McKinley remained dedicated to his eclectic reputation, leaving behind a legacy of music with its unpredictability and grace, much like the knuckleball pitches he once threw during his semi-pro baseball days in Boston.