The Nigerian striker's stay was initially due to end on 31 May but he will now remain with the Reds until 31 January 2021, enabling him to build on an impressive start to life with the club he supported as a boy.
Ighalo's tally of four goals in eight appearances so far includes at least one strike in each of his three starts - against Club Brugge, Derby County (2) and LASK.
Today's confirmation is a timely boost for United boss Ole Gunnar Solskjaer, as he continues to prepare his squad for this month's resumption of competitive football.