By the end of 1920, the Belgian economy being completely destroyed, the young man decided to abandon his plans for higher education, and becomes a civil servant in the Department of Finance. He took lessons in Yoga, and begins to practice respiratory exercises. He also experiments with White Magic. The combination of the two practices, associated with his poor heath, that Gustave describes as a "disallignment" between his physical and higher bodies, resulted in a series of dreaming, sleepwalking, hypnotic experiences lasting for several years, until he developped a controled clairvoyance. He remained quite reluctant to use this faculty until he got more occult training by qualified people. Later he used this gift to help hundreds of his consultants.

Gustave-Lanbert Brahy joined the Theosophical Society in 1924, and its Esoteric Section in 1926. He found there the formal training in spirituality and occultism he was longing for. He came in contact with Bishop Nyssens and joined the Liberal Catholic Church, in which he could enjoy the freedom of thoughts and benefit from the Holy Sacraments. When the leaders of the Society began to promote J. Kishnamurti as the new Messiah, He resigned from it in 1929, but remained a member of the Liberal Catholic Church.

During the Winter of 1926-1927, Gustave young daughter contracted pneumonia, associated with ear infection. In these days, this disease was often fatal. The child seemed to be on the point of dying. Desperately, the parents prayed with fervour. Gustave-Lambert remembered some of his collegues astrologers in California, and sent a cablogram to Rosecrucian Asociation of Oceanside, as last resource. The next day, around 1:00 p.m. the little girl open her eyes, recognized her parents, and fell asleep. She recovered within days. Two weeks later, a letter from Oceanside aknowledged his request for help, and offered him to open a Rosicrucian Temple in Belgium. He started to work on that project after his resignation from the Theosophical Society, in 1929 and served as president of that Temple until 1935.

Having a natural inclination towards precision and exactitude, Gustave-Lambert soon became an able practitionner of Astrology. In 1926, he founded l'Institut d'Astrologie (Astrological Institute) with the purpose to improve the training of Astrologers and to modernize the calculation of native charts and projections . The same year, as an extention of the Institute, he founded his own astrological magazine, named DEMAIN (Tomorrow) in which he began to publish astonishing prediction.

In 1927, Brahy makes a most important encounter that will shape his spiritual and occult career in the person of the Vicomte de Herbais de Thun. This man will not only support Gustave's magazine financially, but also introduce him to the Theosophical Society, and later will initiate him into one of the most discrete branches of Belgian Martinism founded by Augustin Chaboseau . The principles laid out for the Degree of Serviteur Inconnu (Unknown Servant) will guide the young man through his entire life. With two of his Martinist Brothers: Emile Dantine and Emile Ehlers, Gustave-Lambert founded the F.U.D.O.S.I. (Fédération Universelle Des Ordres et Sociétés Initiatiques); Ehlers who owned an occult bookstore, and Gustave didn't want to see their names associated with the new Federation and remained silent partners. After the war was over, Dantinne became dishearted and believed that the Federation couldn't be reassembled, he joined the A.M.O.R.C. and from that moment, the Universal character of the F.U.D.O.S.I. was lost.

In 1932, he defended a thesis establishing the relation between the solar rythms, the planetary rythms, and cosmic phemoma, during the 54th Congress of the French Association for the Promotion of Science. His thesis dealt in part with Astrology, and this part was published separately in a book entitled: Les Fluctuations Boursières et les Influences Cosmiques (Stock Market Fluctuations and Cosmic Influences).

He traveled twice to the USA in 1937 and 1939. In that period, and during World War II, he also published several novels, works about Astrology, and the French translation of works of the English Author Bulwer Lytton.

At the end of WWII, Brahy was a Honorary member of various Scientific Research Societies in Belgium, England, France, Switserland, and the United States. His Magazine DEMAIN was unversally known and appreciated.

In Belgium, Gustave-Lambert associated closely with Choisnard to found the Institut d'Astrologie de Belgique which activity began in November 1926, by a lecture of Paul Choisnard. This Institute provided Astrology with a positive impulse, and specialized in scientifical methods to approach the reality of Astral influences. Monthly predictions were published and daily previsions made, on the fluctuations of shares in the Stock Market.

Frequently, Brahy was submitted to the accusation that associated Astrology with Charlatanism. As a result of his predictions, many investors made such profit in speculting on the Stock Market that legislation was passed in France, and later included also into the Belgian Penal Code, forbidding the publication of Astrological and Spiritual predictions for commercial use, under very severe penalty.

Gustave-Lambert Brahy discontinued the publication of his commercial predictions around 1950, but continued his private practice. He was often consulted by Market specialists, mostly from the USA. Within a few years, the magazine DEMAIN lost its popularity as the long term Stocks predictions would no longer be published. Its publication was discontinued in the 1970's.

Gustave-Lambert Brahy lead also a very discrete spiritual life, as he had anticipated at the end of the Confidences d'un Astrologue, published in 1946:

" My friends may be right: this War is the end of an era. What will follow will never resemble at what preceded it. I feel often, as I am impatient to begin new projects, the the War has made me a new man taking gradually the place of the tormented being I have been sofar. Was all that I have sofar experienced only a prelude? And shall I move, as I believe to have felt, towards a new lifestyle, towards what is simply Life? "
I have the distinctive impression that I can be of better use to humanity, if I don't devote my life exclusively to Astrology. During the last years, I hear an inner calling to join the men of good will working to the moral reconstruction.