In 1953 he was hired by SF Hamborn 07. In his second season with the club from the suburb of Duisburg he led the club to promotion to the western division of the five ways split first division of Germany, the Oberliga West. In 1955, he was appointed as manager by then German champions, Rot-Weiss Essen coaching among others Helmut Rahn there. In the next couple of years he led the team to ranks 4 and 8 in the Oberliga West.
After leaving Rot-Weiss Essen, Schwartz joined the Dutch football association, the KNVB and took on the reins of the Dutch national football team. He guided the team through 49 matches. However, this was in an era when Dutch football had yet to achieve the standing it has held since the 1970s. Results varied extremely and included 7–0 defeat to Germany in 1959 in Cologne, as well as back to back 1–0 wins against France and world champions Brazil in 1963. He held the position of national coach until 1964, when Denis Neville replaced him.
In 1964–65, he coached Portuguese club S.L. Benfica, then with Eusébio. There he led them to their first third-consecutive league title. After this, Benfica overcame Real Madrid in the quarterfinals of the European Cup of Champions and eventually even made it all the way to the final, where Benfica had to yield to the masters of the Catenaccio, the Helenio Herrera coached team of Inter Milan, who won 1–0, thus failing what would be Benfica's third European Cup title.
From July 1965 to June 1968 Schwartz coached – as successor to Ivica Horvat – Eintracht Frankfurt in the German Bundesliga. There he introduced the 4–2–4 system. Nevertheless, place 4 was as good as it got in the league. During the 1966–67 season he won the International Football Cup and the Coppa delle Alpi. In the same year he led his side to the semifinals of the Inter-Cities Fairs Cup. In 1969–70, he coached FC Porto. Not only that the Dragons exited already in the first round of the national cup competition and in the second round of the Inter-Cities Fairs Cup – in the end Porto was only ninth in the league, the club's worst finishing ever.
End of the career in Munich and Strasbourg
In the 1972–73 season, Schwartz coached TSV 1860 Munich, but he could not help them to fulfill their aspirations to return to the Bundesliga after then three years of absence. He had more luck in 1976–77, when in the course of his last professional engagement he led Racing Strasbourg to promotion to the French Ligue 1. After this he guided the Alsatian amateur side SR Haguenau, today's FCSR Haguenau, through the 1978–79 season. Haguenau, he decided, was also a nice place for him to spend the rest of his life.
