Among the professional activities are to be mentioned: Between 1999 and 2003 he held several positions representing the Students of the University of Agronomic Sciences and Veterinary Medicine Bucharest, among which are: In 2006, Daniel Constantin joined the Conservative Party (PC), where he coordinated the work of the European Funds Department.

The Ministry of Agriculture, under the leadership of Daniel Constantin, is in dispute with the Grivco group, controlled by Voiculescu, accusing him of a damage of 60 million euros, following the fraudulent privatization of the Food Research Institute (ICA).

In May 2017, Daniel Constantin and former education minister Sorin Cîmpeanu left ALDE after a conflict with co-chair Popescu-Tăriceanu.

In November 2019, Constantin and six other PRO deputies voted, against Ponta's order, for the new government of Ludovic Orban of the National Liberal Party (PNL).

In early 2020, Constantin alongside Cîmpeanu and three other former PRO lawmakers joined the PNL.