We report the single-crystal synthesis and detailed investigations of the cage-type superconductor Sc₅Ru₆Sn₁₈, using powder x-ray diffraction (XRD), magnetization, specific-heat and muon-spin relaxation (μSR) measurements. Sc₅Ru₆Sn₁₈ crystallizes in a tetragonal structure (space group I4₁/acd) with lattice parameters a = 1.387(3) nm and c = 2.641(5) nm. Both DC and AC magnetization measurements prove the type-II superconductivity in Sc₅Ru₆Sn₁₈ with T_c ≈ 3.5(1) K, a lower critical field = 157(9) Oe and an upper critical field, H_c2(0) = 26(1) kOe. The zero-field electronic specific-heat data are well fitted using a single-gap BCS model, with Δ(0) = 0.64(1) meV. The Sommerfeld constant γ varies linearly with the applied magnetic field, indicating s-wave superconductivity in Sc₅Ru₆Sn₁₈. Specific-heat and transverse-field (TF)-μSR measurements reveal that Sc₅Ru₆Sn₁₈ is a superconductor with strong electron-phonon coupling, with TF-μSR also suggesting a single-gap s-wave character of the superconductivity. Furthermore, zero-field μSR measurements do not detect spontaneous magnetic fields below T_c, hence implying that time-reversal symmetry is preserved in Sc₅Ru₆Sn₁₈.