Vaclík started out with FC Vítkovice in the Czech 2. Liga, where he played for three seasons before transferring to Viktoria Žižkov. Žižkov won promotion to the Czech First League in Vaclík's first season with the club, drawing attention from a number of teams. In July2011, Vaclík signed a three-year contract with Dutch side De Graafschap, however it was later announced that he had failed a medical in the Netherlands and would be returning to Prague. Vaclík played for Žižkov during the first half of the 2011–12 Czech First League. In January 2012, with Žižkov bottom of the league with just seven points from 16 matches, Vaclík transferred to Sparta Prague for a reported fee of 8.25 million CZK, signing a contract to keep him at the club until the summer of 2016.
Basel
In May 2014 Vaclík signed for FC Basel of the Swiss Super League on a four-year contract. He made his first team league debut on 19 July 2014 in the 2–1 away win against Aarau. The season 2014–15 was a very successful one for Basel. The championship was won for the sixth time in a row that season and in the 2014–15 Swiss Cup they reached the final. But for the third season in a row, they finished as runners-up, losing 0–3 to FC Sion in the final. Basel entered the Champions League in the group stage and reached the knockout phase as on 9 December 2014 they managed a 1–1 draw at Anfield against Liverpool. But then Basel then lost to Porto in the Round of 16. Basel played a total of 65 matches. Under trainer Paulo Sousa Vaclík totaled 51 appearances, 33 in the League, 8 in the Champions League, as well 10 in test games. Under trainer Urs Fischer Vaclík won the Swiss Super League championship at the end of the 2015–16 Super League season for the again. Vaclík extended his contract with the club, this is now valid until the end of June 2021. Then at the end of the 2016–17 Super season League Vaclík won the championship for the third time. For the club this was the eighth title in a row and their 20th championship title in total. They also won the Swiss Cup for the twelfth time, which meant they had won the double for the sixth time in the club's history.
Vaclík represented his country at youth level between 2005 and 2011, progressing from the under-16 team up to the under-21 team. Vaclík was involved in the national teamfor the first time in 2011, selected as a third goalkeeper for the squad's matches against Spain and Luxembourg, although he did not play. He made his senior debut for the Czech Republic on 14 November 2012 in a 3–0 friendly victory against Slovakia.
