Lu served the Qing regime as Chinese delegate at the first and second Peace Conferences in The Hague (1899 and 1907), as Minister to Belgium, and as Ambassador to Russia, but he never forgot the imperial government's betrayal of his "second father".

When the 1911 Revolution broke out he was Ambassador in St Petersburg, and he took it upon himself, against the advice of his colleagues at other European capitals, to cable Beijing that there could be no hope of assistance from the Great Powers.

[3] At the proclamation of the Chinese Republic in 1912, he joined the party of Sun Yat-Sen, and served as Foreign Minister in the provisional government under President Yuan Shikai, March 1912 – September 1912.

From 27 January 1915 to 17 May 1916 he served as Minister of Foreign Affairs for a third time, in the "northern" government in Beijing which enjoyed international recognition, undertaking difficult negotiations with Japan[6] and Russia.

At the death of his wife he retired from an active life, and in 1927 became a postulant, under the name Dom Pierre-Célestin, in the Benedictine monastery of Sint-Andries in Bruges, Belgium.

When you have grasped its heart and its strength, take them and give them to China.His planned departure was postponed during the Chinese Civil War, and Dom Lu died in Bruges, Belgium on 15 January 1949.

His best known work, published in 1945, is an autobiography in French, Souvenirs et pensées, summarizing his diplomatic and political career and his subsequent religious vocation, in which Christianity appears as a completion of the Confucian tradition of "pacifying the universe".

The work was translated into English by Michael Derrick as Ways of Confucius and of Christ (London, 1948), and into Dutch by Frans Van Oldenburg-Ermke, under the title Mijn roeping: herinneringen en gedachten (Bruges, n.d.