His father was Chrétien-Charles Haëntjens (1790–1836), who also became a landowner and trader and was passionately interested in scientific research.

[3] During the June Days uprising in 1848 Alphonse Alfred Haentjens fought as a volunteer for the forces of order, and received a bullet in the chest.

In the general elections of 1 June 1863 he ran as candidate for the legislature in the first district of Sarthe with a large majority.

[4] During the French Third Republic Haentjens was a Representative of Sarthe in the National Assembly from 8 February 1871 to 7 March 1876.

He voted in favour of peace with Germany, against the exile of the princes, for the constituent power of the Assembly, for the resignation of Adolphe Thiers, against the government of Albert de Broglie and against the constitutional laws.

[4] Haentjens founded the Appel au peuple parliamentary group late in 1871 to restore the Second Empire's ideals of democratic imperialism and free trade.

They claimed that they were more democratic than the Republicans, they mocked the Monarchists and they opposed Adolphe Thiers in his wish to tear up the low-tariff treaties of the empire.

He continued to be involved in discussions of finance and the budget, and advocated a Bonapartist change of regime.