A native of Nieuwerkerk aan den IJssel, Slob studied history at the University of Groningen.

In 2001, Slob became a member of the House of Representatives for the Reformed Political League (GPV) when its leader, Gert Schutte, retired.

After the 2002 election, the newly formed Christian Union lost a seat and Slob did not return to Parliament.

When Kars Veling, the party's lijsttrekker, stepped down as a result of the election loss, Slob took his place.

After the 2006 general election, Slob and party lijsttrekker André Rouvoet represented the Christian Union in the negotiations for the formation of the new cabinet of the Netherlands, the Fourth Balkenende cabinet; Rouvoet was appointed Deputy Prime Minister of the Netherlands.