High temperature ferromagnetic materials with planar surfaces are promising for spintronics applications. Using the state-of-the-art density functional theory (DFT) calculations, we predict a new phase of the carbon-nitride monolayer (gt-C3N3). Furthermore, pure and first-row transition metal (TM = Sc to Cu) embedded carbon nitride (TM@gt-C3N3) systems are studied for possible spintronics devices. Such Cr, Mn and Fe embedded gt-C3N3 systems show excellent dynamical, thermal and mechanical properties. High temperature ferromagnetism and high magnetic anisotropy energy (MAE) are envisaged in Cr, Mn and Fe incorporated gt-C3N3 systems. We find that Cr@gt-C3N3 is a ferromagnetic material with a Curie temperature of ∼338 K. The calculated magnetic anisotropy energy (MAE) in Cr@gt-C3N3 is 4.02 meV per Cr atom, which can be increased to 23.69 meV per Cr in the presence of an external electric field (ϵ). Thereby, such a material with high MAE can be very promising for spintronics device.