Measurements of the time-dependent $C\!P$-violation observables in $B^0\!\to D^\mp\pi^\pm$ and $B^0_s\!\to D_s^\mp K^\pm$ decys are reported. The decays are reconstructed in a dataset collected with the LHCb experiment in $pp$ collisions at centre-of-mass energies of $7$ and $8\,\text{TeV}$ corresponding to an integrated luminosity of$ 3\,\text{fb}^{-1}$. For $B^0\!\to D^\mp\pi^\pm$ decays, the $C\!P$-observables are measured to be $S_f = 0.058 \pm 0.020 \pm 0.011 $ and $S_{\bar{f}} = 0.038 \pm 0.020 \pm 0.007$. For $B^0_s\!\to D_s^\mp K^\pm$ decays, $C_f = 0.730 \pm 0.142 \pm 0.045 $, $S_f = -0.519 \pm 0.202 \pm 0.070 $, $S_{\bar{f}} = -0.489 \pm 0.196 \pm 0.068$, $A_f^{\Delta\Gamma} = 0.387 \pm 0.277 \pm 0.153$ and $A_{\bar{f}}^{\Delta\Gamma} = 0.308 \pm 0.275 \pm 0.152$ are determined, where the first uncertainties are statistical and the second systematic. Using these observables the CKM angle $\gamma$ is constrained at \SI{68}{\percent} CL to be $[5,86]{}^{\circ}$ and $\left(128^{+17}_{-22}\right)^{\circ}$ modulo $180^\circ$ for $B^0\!\to D^\mp\pi^\pm$ and $B^0_s\!\to D_s^\mp K^\pm$ decays, respectively.