A possible route to realize fault-tolerant quantum computing is to find unconventional superconductors, where superconductivity coexists with nontrivial band topology. In this work, we report such a possibility in $6R-{\mathrm{SnNbSe}}_2$ obtained by Sn intercalation into ${\mathrm{NbSe}}_2$. Rietveld refinement confirms a centrosymmetric crystal structure with space group $R\overline{3}m$. Structural, electronic, and magnetic measurements confirm the emergence of a superconducting phase with a transition temperature $T_c\approx 4$ K. The temperature dependence of the upper critical field $H_{c2}\left(T\right)$ is well described by a two-band model. Temperature-dependent magnetic penetration depth and superfluid density measurements are performed using the tunnel diode oscillator technique. Our analysis implies the mixing of nodal and nodeless order-parameter symmetry in $6R-{\mathrm{SnNbSe}}_2$. Such results are surprising for a centrosymmetric superconductor but are consistent with theoretical predictions of topological nodal-line features in ${\mathrm{SnNbSe}}_2$. Thus, $6R-{\mathrm{SnNbSe}}_2$ emerges as an interesting platform for exploring unconventional pairing mechanism in transition metal dichalcogenide superconductors.

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• Superconducting RF
• Superconducting order parameter
• Topological superconductors
• Transition metal dichalcogenides