Franz Lehar was born on April 30, 1870 in Komarom Hungary to Franz Lehar senior, a military bandmaster and composer, and Christine Neubrandt. Being born into a musical house, Franz learned to play the violin and piano before he could read or write. His mother encouraged free improvisation on the piano, and by age eleven, Franz had composed his first lied. Franz then attended the conservatory of Prague for six years.

In the summer of 1888, Franz began his first musical engagement in Barmen-Elberfeld and worked his way up to concertmaster. However, he did not enjoy all the concerts because it left no time for him to compose. To get out of this predicament, his father arranged his draft into the army. Franz began his military service in the band of the infantry regiment #50 conducted by his father. Father and son did not always agree, so Franz left and found a post as the bandmaster of the 25th infantry in Losoncz. Beginning in 1890 and for the next twelve years, Franz was a military bandmaster. To supplement his pay, Franz made band arrangements of folk songs, classical pieces and popular songs. In 1894, Franz was discharged from the military after an "incident" in which he did not follow his commanding officer's order to conduct a concert to the end. So Franz conducted the naval band in Pola, the naval port of the monarchy. In Pola, Franz met the poet Felix Falzari and began a collaboration to create his first opera Kukuschka. Publishers began to take interest in Franz, who gave up his post hoping to make his living as a composer. Unfortunately, while Kukuschka met with some popular success with the public, it failed to become the breakthrough that Lehar was looking for. So Lehar took up the military bandleader post in Triest and in 1898, Franz took the former post of his father for the infantry regiment #87 in Budapest. He eventually transferred to Vienna in 1899 as the bandmaster of the infantry regiment #26 and in 1902, he composed the waltz Gold and Silver that garnered him some of the international fame that he sought. Later that same year, Lehar gave up the military for good and received the position of musical director at Vienna's Theater an der Wien.

Franz began a friendship with Viktor Leon, a noted librettist and one of the most important and successful personalities of the Viennese operetta scene. Leon gave Franz a libretto for the operetta Der Rastelbinder that was accepted by the Carl-Theater, a direct competitor with the Theater an der Wien. This dual role as composer at large and conductor at the Theater an der Wien soon ended in 1902, but the real fame for Lehar was just around the corner.

Already a well-known character around Vienna, Lehar announced his new work to be produced for the Theater an der Wien on December 30, 1905 as Die Lustige Witwe (The Merry Widow). The libretto was written by Viktor Leon and Leo Stein after Henri Meilhac's comedy Der Gesellschaftsattache. The operetta met with an instant success among the public (although the critics were divided) and was on the program almost continuously until March 1907. By April 1907, The Merry Widow celebrated its 400th performance. Later in 1907, The Merry Widow was performed in London and New York, with performances in 1908 in Copenhagen, Moscow and Milan; 1909 in Madrid and Paris and in 1910 in Brussels.

After the success of The Merry Widow, Franz no longer needed to worry about composing for a living. The royalties alone made him a wealthy man and he soon purchased a summer home in Bad Ischl, the playground of the wealthy. It was in Bad Ischl, that Franz met Sophie Meth, the daughter of a Viennese carpet dealer and already married. In 1906, they began a love affair that ended with Sophie's eventual divorce from her husband and subsequent marriage to Lehar in 1921. Although married, Franz insisted on maintaining his original style of autonomous living and insisted on separate apartments.

Lehar continued to write operettas although none achieved the same success as The Merry Widow. Throughout 1909 and 1910, he composed Peter und Paul im Schlaraffenland, Der Mann mit den drei Frauen, Das Furstenkind, Der Graf von Luxemburg and Zigeunerliebe. The latter three operettas gained in fame throughout the Viennese theaters in record breaking fashion. In three Viennese theaters during 1910, Lehar's operettas were performed 200 times in each.

During World War I, Lehar continued to compose operettas, lieder cycles, and symphonic poems. However the operetta scene was somewhat stagnant during this time of war. After the war, Lehar began an experimentation phase in search of new musical forms. Lehar also began a friendship with Giacomo Puccini that began in 1920 during a visit to Vienna by Puccini. Although Puccini's admiration for Lehar's work was genuine, Franz was greatly affected by the rejection of his work by Richard Strauss. In 1940, Strauss stated that "The danger, which threatens our whole cultural level by Lehar and his companions and to which it has already succumbed for the most part, can not be settled anymore with noble disregard."

In 1921, Lehar would begin a friendship that would dramatically effect his compositional life; he met the famed tenor Richard Tauber. Tauber's interpretation of Lehar's work entranced the composer as well as the public. During the remainder of the 1920s, Lehar wrote for Tauber's voice in the operettas Paganini, Der Zrewitsch and Das Land des Lachelns.

In 1933, Lehar composed Giudetta, a full fledged comic opera, which became Lehar's final work. During his final years, Lehar devoted himself to the Glocken-Verlag, a publishing house he founded in 1935. During World War II, Franz and Sophie faced a most difficult situation given that Franz had cooperated with Jewish librettists, and Sophie had Jewish originas. Fortunately for the Lehars, Hitler was an admirer of The Merry Widow so they escaped the brutality of the Nazi regime. Not so for Lehar's librettists, Fritz Grunbaum and Fritz Lohner who were eventually murdered in concentration camps. Franz and Sophie spent the remainder of World War II at their home in Bad Ischl, while their home in Vienna was ransacked. After a visit to Zurich to see Richard Tauber, Sophie died in 1947. In the summer of 1948, Franz returned to Bad Ischl to settle his estate. He gave his villa to the city of Bad Ischl on the condition that they turn it into a Lehar museum. Franz Lehar died on October 24, 1948. In 1958, a monument dedicated to the composer was created in Bad Ischl and the theater in the town is named after him.