McDaniel was born to musical parents (a vaudeville tenor-turned-storekeeper and a music teacher) who soon became aware of his talent; from the age of nine he took systematic lessons in singing, piano and percussion and enjoyed considerable local popularity as a boy soprano soloist in churches and private concerts. When his voice changed from soprano to baritone, he studied voice first at the University of Kansas, and from 1950 at the Juilliard School of Music in New York as a student of the famous baritone and voice teacher Mack Harrell. After graduating from Juilliard with honors, he was among the first young singers to go to Germany on a Fulbright scholarship in 1953. He studied with Alfred Paulus and Hermann Reutter at the Stuttgart Music Conservatory, working on his already extensive repertoire of German and French art song and making his first professional appearances as a recitalist. Hermann Reutter – a renowned composer in his own right – was to become one of his favorite accompanists throughout his career. After a first contract with the opera of Mainz (1954 – 1955), he had to put his budding operatic career on hold for two years to serve his military service in the U.S. Army; from 1957 to 1958 he was under contract with the Stuttgart State Opera, and from 1959 at the opera of Karlsruhe. It was there that in autumn 1961 Egon Seefehlner, the deputy director and talent scout of the newly reopened Deutsche Oper Berlin, heard him in a performance and recruited him for his opera.
McDaniel remained under contract with the Deutsche Oper from 1962 till 1999, appearing in productions of some of Germany's most distinguished stage directors such as Gustav Sellner, Götz Friedrich or Günther Rennert, in an ensemble that included names like Dietrich Fischer-Dieskau, Elisabeth Grümmer, Josef Greindl, Ernst Haefliger, James King, Pilar Lorengar and Edith Mathis. His stage repertoire of 98 roles encompassed Gluck and Mozart, Italian Bel canto and Richard Strauss as well as contemporary opera (many of these parts he performed for the first time on stage).
He displayed remarkable versatility as an oratorio singer and recitalist, with compositions running the gamut from Baroque to Contemporary. His focus in sacred music was on Johann Sebastian Bach (cantatas, Christ in both the St Matthew Passion and the St John Passion) and Georg Philipp Telemann, with art song it was on Franz Schubert's great song cycles, Robert Schumann, Johannes Brahms and Hugo Wolf. But he was also a frequent performer of French Mélodies, e.g. by Claude Debussy, Maurice Ravel or Francis Poulenc, and something of a specialist of contemporary scores by composers such as Aribert Reimann – his other long-standing musical partner, Hermann Reutter, Anton Webern, Günter Bialas, Luigi Dallapiccola, Carl Orff, and many others.
In addition to his more than 2,100 stage and concert performances in Berlin, he gave frequent guest performances and recitals e.g. in Vienna, Hamburg, Frankfurt, Munich (he appeared regularly at the Munich Opera Festival for 11 years), Geneva, Amsterdam, Mexico and Japan. In 1964 he sang Wolfram in Tannhäuser at the Bayreuth Festival, and in 1971 the male lead in the world premiere of Aribert Reimann's opera Melusine at the Schwetzingen Festival, in 1972 he made his debut as Pelléas in Pelléas et Mélisande at the New York Metropolitan Opera. In addition to these live appearances (3400 in total), McDaniel made between 1954 and 1984 hundreds of recordings of art songs, sacred music and opera repertoire for various radio stations, and starred in TV productions of operas and operettas in the 1960s and 1970s.
In 1970 he was awarded the title of ”Berliner Kammersänger” by the Senate of Berlin.
In the late 1980s, McDaniel began to cut back on his opera and concert performances and finally retired in 1999, after a series of solo concerts dedicated to the popular songs of his native country. He lives in Berlin.
McDaniel's voice was a lyric baritone with a range of 2½ octaves (from a low F in the St John Passion to a high A in Pelléas et Mélisande), a remarkable vocal technique and breath control (he was able to sing the 9-bar melisma in the opening phrase of the Kreuzstabkantate BWV 56 in one breath), and a striking beauty of tone. The New Grove Dictionary of Music and Musicians praises his "mellifluous voice" as well as "a fine sense of line and an acute understanding and projection of the text". The renowned weekly paper Die Zeit commented on his part in Melusine in 1971: "Such poetic vocal expression, such lucid operatic lyricism is unequalled today, and who could give it a more beguiling voice than Barry McDaniel." Over the years the voice gained in nuances and depth of expression but never lost its youthful, lyrical character, and McDaniel always avoided straying beyond the limits of his Fach, e.g. to heavy Wagner or Italian Verismo parts.
McDaniel's recordings span his entire repertoire and all phases of his career. Some of them are commercially available: cantatas and oratorios by Johann Sebastian Bach, operas by Mozart, Strauss, Weill and Henze and works of contemporary church music (many of which he was the first and only to commit to record). Although his commercial recording career as a song performer was hampered by the overwhelming competition, on a limited market, from his two great German contemporaries Hermann Prey and particularly Dietrich Fischer-Dieskau, he recorded the Winterreise twice (1972 and 1985) for commercial labels and sang a vast number of art songs for nearly all West German public radio stations, the Swiss radio and the BBC. There exists also a 1972 live recording from the Metropolitan Opera which documents his Pelléas – one of his greatest operatic roles, and hailed by the distinguished critic Hans Heinz Stuckenschmidt in 1963 as "a performance of perfection".