On 10 August 2018, Mbulu signed a one-year contract with Motherwell after his release from Millwall at the end of the previous season. In October 2018, Mbulu was named as Player of the Round for the third round of the Scottish Challenge Cup after scoring to help Motherwell's under-21 side to a 2–0 win against League of Ireland club Sligo Rovers. Mbulu made his league debut for Motherwell on 11 November, when he came on as a second-half substitute in the 77th minute of a game against Rangers at Ibrox. On 9 December, two Hearts supporters were arrested on suspicion of racially abusing Mbulu during a match at Tynecastle. On 21 May 2019, Motherwell confirmed that Mbulu would be released at the end of his contract on 31 May 2019.
