The 1920s also marked the club's first ascension to the national level, competing in the Western German championship after claiming the crown in the district league four times in a row.

After World War II, the club initially could not match its pre-war successes until it won the German amateur championship in 1955 with a stunning 5–0 win over 05 Bad Homburg.

Six years after winning the German amateur championship, Sportfreunde Siegen made the jump to professional football in 1961.

League games against renowned clubs such as Bayer Leverkusen, Fortuna Düsseldorf or Borussia Mönchengladbach were common during these days.

After some years of struggle, Sportfreunde Siegen fought its way back to professional football in 1972, claiming the West German amateur championship and promoting to the second-tier Regionalliga once again.

After several ups and downs in the late 1980s and early '90s, the club made it back to third-tier Regionalliga in 1997, narrowly missing out on the promotion to the 2.

In the same year, the team advanced to the quarter-finals of the DFB-Pokal, the German cup, before losing to Bundesliga side VfL Wolfsburg in a highly contested match.

The following season saw the refurbishment of Leimbachstadion, the club's home ground since 1957, to its current capacity of 18,700 and quite decent results in the first half of the 2005–06 campaign in the 2.

The team finished second-last in the Regionalliga in 2015 and was relegated from the league but bounced back immediately by winning the Oberliga Westfalen championship.