It was the result of the decision of an already existing nationally oriented group (called the Old Slovak School) that wanted to take part in the elections to the Hungarian Diet (parliament).
The first successful year from this point of view was 1901, when the SNS received four mandates in the Hungarian parliament.
Since then, all Slovak political movements (the original members, the Catholic ľudáci and the liberal Hlasists) except the Social Democrats were included in the party.
On 28 June 1911, deputies of the party submitted a document called Memorandum of the SNS to the Hungarian government.
In this document the SNS demanded the practical implementation of the so-called Nationalities Law from 1868 (the law declared all citizens of the Kingdom of Hungary members of a single Hungarian [in Hungarian "Magyar"] nation and Hungarian the only state language; the minor educational, administration and church rights for non-Hungarian nationalities stipulated in the law were never implemented), the permission to use the Slovak language in some types of schools at least and the returning of the property of the dissolved Matica slovenská.
The ideology was supported by a majority of the relevant Czechoslovak political parties and by the president, Tomáš Masaryk.
SNS not only demanded an acceptation of the Slovak nation's existence, but also a political autonomy for Slovakia.
The nationalist wing returned to its original name Slovak National Party.
In another election year, 1929, the party participated in the elections as a member of a multi-ethnic coalition of parties (Czechoslovak National Democracy, SNS and an ethnic Rusyn Russophile block), which received 359 547 votes and 15 mandates.
A group of SNS members (e.g. M. Daxner, Ján Paulíny-Tóth) didn't agree with this coalition.
This step was supported also by other parties (including the SNS) on the same day in the Žilina Treaty and then accepted by the government in Prague.
This step was forced by the People's Party and supported only by a group of members around Miloš Vančo.