Mercury wrote 10 of the 17 songs on Queen's Greatest Hits album: "Bohemian Rhapsody", "Seven Seas of Rhye", "Killer Queen", "Somebody to Love", "Good Old-Fashioned Lover Boy", "We Are the Champions", "Bicycle Race", "Don't Stop Me Now", "Crazy Little Thing Called Love", and "Play the Game". In 2003 Mercury was posthumously inducted into the Songwriters Hall of Fame, and in 2005 he was posthumously awarded an Ivor Novello Award for Outstanding Song Collection from the British Academy of Songwriters, Composers and Authors.
The most notable aspect of his songwriting involved the wide range of genres that he used, which included, among other styles, rockabilly, progressive rock, heavy metal, gospel, and disco. As he explained in a 1986 interview, "I hate doing the same thing again and again and again. I like to see what's happening now in music, film and theatre and incorporate all of those things." Compared to many popular songwriters, Mercury also tended to write musically complex material. For example, "Bohemian Rhapsody" is non-cyclical in structure and comprises dozens of chords. He also wrote six songs from Queen II which deal with multiple key changes and complex material. "Crazy Little Thing Called Love", on the other hand, contains only a few chords. Despite the fact that Mercury often wrote very intricate harmonies, he also claimed that he could barely read music. He wrote most of his songs on the piano and used a wide variety of key signatures.
Mercury was noted for his live performances, which were often delivered to stadium audiences around the world. He displayed a highly theatrical style that often evoked a great deal of participation from the crowd. A writer for The Spectator described him as "a performer out to tease, shock and ultimately charm his audience with various extravagant versions of himself." David Bowie, who performed at the Freddie Mercury Tribute Concert and recorded the song "Under Pressure" with Queen, praised Mercury's performance style, saying: "Of all the more theatrical rock performers, Freddie took it further than the rest... he took it over the edge. And of course, I always admired a man who wears tights. I only saw him in concert once and as they say, he was definitely a man who could hold an audience in the palm of his hand." Queen guitarist Brian May wrote that Mercury could make "the last person at the back of the furthest stand in a stadium feel that he was connected"
Mercury played the piano in many of Queen's most popular songs, including "Killer Queen", "Bohemian Rhapsody", "Good Old Fashioned Lover Boy", "We Are the Champions", "Somebody To Love", and "Don't Stop Me Now". He used concert grand pianos and, occasionally, other keyboard instruments such as the harpsichord. From 1980 onward, he also made frequent use of synthesisers in the studio. Queen guitarist Brian May claims that Mercury was unimpressed with his own abilities at the piano and used the instrument less over time because he wanted to walk around onstage and entertain the audience. Although he wrote many lines for the guitar, Mercury possessed only rudimentary skills on the instrument. Songs like "Ogre Battle" and "Crazy Little Thing Called Love" were composed on the guitar; the latter featured Mercury playing rhythm guitar on stage and in the studio.