Holst left college in 1989, playing the trombone in the Carl Rosa Opera Company and later Scottish Opera. The cramping neuritis in his right hand was perpetually defeating him as a keyboardist. He could no longer practice for long hours and he realized that he could not keep up his technique. He therefore decided to take up the trombone, which allowed him to play in orchestras and provide him with an income. The experience was also of use to him as a composer.
In 1901, Holst married Isobel Harrison, and they lived in their first home together in Shepherds Bush. He came into a small legacy when his father died, so he and Isobel went to Berlin for a holiday. When Holst returned to London, he vowed to give up the trombone and concentrate in his composing. He became disappointed because he wrote many good songs, but they were constantly refused by publisher after publisher. His wife copied his music and also made clothes for her friends just to make ends meet. Just as Gustav was starting to lose hope, he was asked to deputize for the singing teacher at James Allen School in Dulwich. His career as a gifted teacher had begun.
In 1905, Holst was appointed Director of Music at St. Paul's Girls School in Hammersmith after teacher in Dulwich for two years. He would stay at this girls school until the end of his life. His heavy and exhausting teaching schedule meant that the time left available for composition was often fragmented. But during this time, wrote pieces such as The Cloud Messenger and St. Paul's Suite in 1913, Dona Nobis Pacem, The Hymn of Jesus in 1917, and The Planets, which took Holst two years to write (1914-1916). This piece gave him his big break, even though he never considered it to be his best. His immediate success was part of the source of his consternation. Life for him was gradually becoming easier by the end of 1922. For the first time ever, he had earned more than one thousand pounds a year.