A galvanometer acting as a voltmeter will have :-

A voltmeter is connected in parallel across the part of the circuit whose potential difference is to be measured.
It should draw almost no current from the circuit, otherwise it would change the very potential difference it measures. So a voltmeter must have a very high resistance.
To convert a galvanometer of resistance $G$ into a voltmeter of range $V$, a high resistance $R$ is connected in series with its coil, such that $V = I_g(G + R)$, i.e. $R = \dfrac{V}{I_g} - G$.
(A low resistance in parallel, i.e. a shunt, converts a galvanometer into an ammeter instead.)
So a galvanometer acting as a voltmeter has a high resistance in series with its coil.