In 1876, Philippe Pétain is 403rd of 412 at the Saint-Cyr Special Military Academy. He leaves there, in 1878 (Graduating class De Plewna), 229th of 386 student-officers and chooses to serve in the infantry.

His career is henceforth characterized by metropolitan garrisons: Villefranche-on-Sea, Besançon, Marseilles, Amiens, Châlons-sur-Marne, Quimper, Saumur, Arras, Saint-Omer, Paris. Second-lieutenant in 1878, he is a lieutenant in 1883, captain in 1890, commander in 1900, lieutenant-colonel in 1907 and colonel in 1910. Relatively slow advancement, ascribable to an uprightness not very compatible with those of an epoch in which, as Bainville notes in his History of France, « an on-file denunciation was organized against officers who went to mass». Pétain, himself, was annotated in 1903: « Went to the War School, unknown, but new and serious information show him to profess nationalist and clerical ideas ».

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His first garrison, in 1878, is Villefranche-sur-Mer. It serves on the 24th Infantry Battalion (Battaillon de chasseurs à pied (BCP). Elite marksman, he is a fencer said to be the equal of a provost marshal, and untiring marcher, and a horseman of first order. He is, to men of his unit, a radiant example. He shares their exercises and their pain. He learns to know more intimately those who, in their great majority, are as himself, a product of the land. He knows instinctively that to lead men whose vocation is to fight, it is necessary to like them, and if not, to respect them.

Such is the secret of the man who will be successively officer of troops and headquarters staff officer, General, General in Chief, Marshal of France, then Head of State.

In 1883, he is assigned, to Besançon, with the 3rd BCP where he devotes his moments of leisure to the preparation of the entrance examination to the Higher War School. He is allowed entrance there in 1888. Two years of studies will enable him to look further into his military culture, and to realize that the doctrines taught do not take fire power and the vulnerability of infantry sufficiently into account.

Promoted captain in 1890, he is assigned to the staff of the XV Corps, in Marseilles, where he is noted to be : « Quiet, cold, calm, opposed to too prompt decisions, and always proceeding in an orderly way. » He joins, in 1891, 29th BCP at Vincennes. In 1895, he is at Paris headquarters, from where he will be transferred, in 1899, to the 8th BCP at Amiens.
Meanwhile, he obtained, in 1897, a certificate as a balloon pilot. That is to say, he belongs to a restricted circle of the first flying men. He will be soon, along with Colonel Barès and General Duval, the promoter of the aerial weapon and its use in battle on the ground.
Promoted battalion chief in 1900, he is named instructor at the Teacher Training School for marksmanship at Châlons-sur-Marne. His teaching not being in agreement with the ideas of the commander of the School, he is transferred, in 1901, to the 5th Infantry Regiment in Paris, where, in his capacity as assistant professor at the Higher War School, he is in charge of the courses in applied infantry tactics. He is then proclaimed Knight of the Legion of Honour.

After a short assignment with 10th I.R., he resumes, from 1904 until 1907, his courses at the Higher War School. Appointed lieutenant-colonel in 1907, he is assigned in Quimper to the 118th I.R.

His qualities as a professor are so appreciated that he is again affected, in 1908, to the Higher War School to hold the chair of applied infantry tactics. General Bonnal, commander of the School, considers him, « a first-rate person. (…) Brings together the qualities of strength of character, a keen eye, and intelligence, in the right proportion, that being a desirable quality for a future great chief ». His successor, Foch, also judges Pétain eulogistically: « Man of the highest sentiments, of an extraordinary uprightness of character, of a very clear and precise intelligence, of a rigorous method, having a fail-safe conscience, a very precise tactical sense, and a profound knowledge of weaponry (…) he develops at this school an educational program of first order from all points of view. »

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Promoted colonel in 1910, Philippe Pétain studies at the CHEM (Center for High Military Studies) then teaches general tactics at the Cavalry School at Saumur. At the end of 1912, he takes command of 33rd I.R. in Arras, where Second-lieutenant Charles de Gaulle is affected upon graduation from Saint-Cyr. Each holds the other in esteem. Pétain takes note of de Gaulle : « He left Saint-Cyr Military Academy as 13th of 211 students, he affirms himself from the very start, just as an officer of real value which gives the greatest hope for the future (…) Very intelligent, passionately likes his profession (…) worthy of all praises. » As for Gaulle, he will write in his memoirs: « After Saint-Cyr Military Academy, I had my learning experience as an officer with the 33rd I. R. at Arras. Pétain, my first colonel, showed me the worth of the gift and the art of commanding. »
In March 1914, colonel Pétain takes command by interim of the 4th Brigade at Saint-Omer. As the head of this unit, he is engaged in the conflict which bursts out on August 3, 1914. Conflict during which he will climb all the levels of command, to finally head the French Armies, crowned by his rise to the dignity of Marshal of France.