The Herd are the G League affiliate for the Milwaukee Bucks—who selected Jennings 10th overall in the 2009 draft.
"We couldn't be more excited to welcome Brandon back to the Bucks organization and introduce him to the Herd family," Herd general manager and Bucks vice president of basketball operations Dave Dean said in a team statement. "Brandon has played at the highest levels all over the world, and we look forward to him calling Oshkosh home."
Jennings, 28, most recently suited up for the Shanxi Brave Dragons of the Chinese Basketball Association.
In 13 appearances overseas, he averaged 27.9 points, 6.8 assists, 5.0 rebounds and 2.7 steals per game while shooting 43.2 percent from the field and 38.2 percent from three.
After signing with the Wizards, Jennings averaged 3.5 points and 4.7 assists a night in a backup role behind John Wall. However, his stock plummeted as he shot 27.4 percent from the floor.
Jennings' inefficient production continued in the postseason.
Appearing in all 13 of Washington's playoff games a year ago, he mustered 2.8 points and 1.8 assists per outing with a 38.9 percent conversion rate from the field and a 2-of-13 showing on three-point attempts.
Jennings hasn't been the same player since he tore his Achilles in January 2015, but the Bucks could use him in a pinch with Malcolm Brogdon (quad) and Matthew Dellavedova (ankle) both sidelined into March.