A strictly orthodox theologian and a clear writer, Luthardt became widely appreciated as the author of apologetic lectures. These were collected under the title Apologie des Christentums (vol. i., 1864, 14th ed. 1896; vol. ii. 7th ed., 1901; vol. iii. 7th ed., 1898; vol. iv. 2nd ed., 1880), a work of which the first three volumes have been translated into English. In 1868 he founded and edited the Allgemeine evang.-lutherische Kirchenzeitung, with its supplement, the Theologisches Litteraturblatt, and in 1880 became editor of the Zeitschrift für Kirche, Wissenschaft und kirchl. Leben.
His other works include Das Johanneische Evangelium erklärt (1852–1853; 2nd ed. in 2 vols., 1875–1876), Offenbarung Johannis erklärt (1861), Lehre von den letzten Dingen (1861; 3rd ed 1885); Kompendium der Dogmatik (1865; 9th ed., 1893), Geschichte der christlichen Ethik (2 vols., 1888–1893), Gnade und Wahrheit (1874) Das Wort des Lebens (1877) and Gnade und Frieden (1880). His autobiography was published with the title Erinnerungen aus vergangenen Tagen (1889; 2nd ed., 1891).