"he briefly joined" is an acceptable phrase in written English.
You can use it in a situation where someone joined something for a short period of time. For example: "He briefly joined the tennis team but soon realized it wasn't for him."
Later, at the Sorbonne, he briefly joined the communist party and was a leader in the anti-colonial student movement.
At Princeton, in 1949, he briefly joined the local Communist Party cell, which had two other members: a cleaning woman and a gardener, he told an interviewer.
During the 1920s he was associated with the Surrealists, and in 1930 he briefly joined the short-lived abstract artists' Cercle et Carré ("Circle and Square") group.
In what one imagines was a moment of student inebriation, he briefly joined the boyband Hyrise, who were longlisted as the UK's Eurovision entry in 2004.
He briefly joined Lionel Hampton's band in 1946 and then entered the Westlake College of Music in Los Angeles to study ear training.
In 1977, he briefly joined a gimmicky made-for-TV international league, which had colored uniforms and white cricket balls; he left with a fat bank account and a global brand name.
After a year, she briefly joined a technology company as a consultant.
In 1933 she won a fellowship to the University of Florence, where she briefly joined the Fascist student movement.
Another biographer, Gerd Langguth of the University of Bonn, related that she briefly joined a West Berlin family at their home.
Then she briefly joined the Experimental Theatre at Vassar College and took dance lessons and performed in New York City.
He said he then briefly joined the Mormon Church, heartened by promises from several Mormon men he befriended that they would help him "find a wife".
