Marius van 't Kruijs came from a musical family. His father Jan van 't Kruijs was organist, carillonneur, choir conductor and music teacher in Oudewater. In Oudewater the young Marius gave public concerts as a five-year-old. He graduated with Willem Nicolaï at the Royal Music School in The Hague at the age of twenty.
In 1881 he settled in Winterswijk. In 1884 he was appointed successor to the composer Samuel de Lange Sr. as organist of the Rotterdam Grote or Sint-Laurenskerk.
In Dutch music life at the end of the 19th century, Van 't Kruijs played an important role, not only as an organist and choir conductor, but also as a composer.
He was conductor of the Groninger Orkest Vereeniging from 1897 to 1905. He wrote organ music and vocal works, the latter often on Dutch texts. That was special in that period, because German and French languages often had priority in art music.
His first opera The Flower of Iceland was performed in 1891 by the Hollandsch Opera Company of Cornelis van der Linden. The alto Cornélie van Zanten sang one of the leading roles.
Due to problems with Van der Linden's company Van 't Kruijs' second opera De Watergeuzen was never performed. He further wrote the De Ruyter Cantate and a cantata in honor of the wedding of Queen Wilhelmina.
From his hand are also Exercises for first-beginner for organ or harmonium as well as 50 pedal exercises.
In 1911 he left for Montreux, hoping to escape from the Dutch musical life. He died in Lausanne without having made a name abroad.
Although he was a contemporary of Gustav Mahler, Richard Strauss, Arnold Schönberg and Igor Stravinsky, his music was too old-fashioned for that.