In 1973, Scottish Rugby formed the official league system. From this and historical results , Musselburgh were placed in Dvision 3. However, the club suffered multiple relegations, ending up in Division 5 in 1975. President Chris Barclay Smith rallie the club at the AGM that year to decide the path in which the club should take. Alec Stewart was appointed head coach that year, remaining in the fifth division before being promoted in 1977, followed by promotion to Division 3 in 1979 and eventually Division 2 in 1981.

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During this time, the club expanded in it's efforts to find the next generation of young talent in the town. Musselburgh Colts were formed in 1974 and still runs to this day, producing many players who have gone on to represent the club and also at international age grade for their country.

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The club at the same time also invested in more developments around the club. It was decided that the changing facilities at the Community Centre were outdated and not that of a club who were pushing for the top. In 1983, the new changing facilities were built which stood until 2021.

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The club remained around either the second or third division for the next few years until 1987, where for the first time in the club's history, they were promoted to the Scottish First Division, at a time when the game was all amateur and many international players played for their club. Clubs in the league at this time included Hawick, who had multiple British and Irish Lions capped players, Heriot's, Kelso and Watsonians. The club drew their first game against Stewart's Melville, then lost to Boroughmuir before beating Kilmarnock and West of Scotland, before a losing run of six games. Despite a win over Ayr 9-4, they could not beat Wastonians on the final day to stay up and were relegated back to Division 2 after one season.

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Not long after winning promotion to the first division, the club had success on the Sevens circuit. One of the highlights for   the team was winning their first home Sevens tournament in 1987, 30 years after last winning the tournament.

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The club over the next few years pushed for promotion back to the top division without any major success. In 1992/1993, it came down to the final game against Stewart's Melville at Inverleith, with the winner gaining promotion to the top flight. The game ended 17-14 to the hosts, who despite ending up on the same amount of points as Burgh, went through thanks to their superior points difference.

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In 1992, the club took their first major overseas tour as they visited Canada in a successful event for the club and the players.

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The club finished the 1996 season with their 75th anniversary against their usual celebration opponents Hawick, losing in a narrow friendly.

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