Joseph will report to Triple-A New Orleans, while the Marlins designated outfielder Brent Keys for assignment to make room for Joseph on the 40-man roster.
The 26-year-old has just seven big-league appearances, posting an 8.53 ERA in brief stints the past two seasons. In one 2014 outing on June 16, he allowed six runs on five hits with two strikeouts and a walk in 2/3 innings.
In 2013, Joseph did not give up a run in six outings over 5 2/3 frames, even finishing two games for the Royals. He is a former third-round selection by the Cincinnati Reds in the 2009 First-Year Player Draft. He was acquired in the Jonathon Broxton trade.
With Triple-A Omaha, Joseph was 1-1 with a 3.86 ERA in 19 games with 30 strikeouts and 20 walks. MLB.com ranked him the organization's 13th-best prospect. He has the stuff to be a closer, but his command is an issue.
Keys was batting .238 with a .371 on-base percentage, two doubles, one triple and 10 RBI in 40 games for Double-A Jacksonville. Last season, he combined to hit .341 between Single-A Jupiter and the Suns en route to Florida State League Player of the League honors by TOPPS.
The 23-year-old was a 17th round pick in 2009 and a top-10 prospect for the organization. He went 4 for 10 with three extra-base hits and three RBI during spring training.
Miami has tried shoring up its bullpen since early-season struggles. It ranks 11th in the National League with a 3.58 ERA and second with 266 1/3 frames. The Marlins traded their Competitive Balance A pick for righty Bryan Morris of the Pittsburgh Pirates in early June. He has yet to give up an earned run. Right-hander Kevin Gregg signed a deal a few weeks ago and is pitching in late-inning situations.
Is this move to help a taxed bullpen in need of an extra arm? Miami has played in five games of 13 innings or more this month and lost each time. Lefty Brian Flynn and righty Sam Dyson have been call-ups for that reason. Righty A.J. Ramos, who has appeared in key situations, has not thrown since tossing 50 pitches in Thursday's 14-inning loss in Philadelphia.