The former Hull City boss will now take charge of their FA Cup third-round clash against Nottingham Forest on Saturday.
But Brown, who has signed a deal until the end of next season, insist his No 1 priority is staying in the Championship. Preston are currently bottom of the table.
Waiting in the wings: Brown is set to take over at Preston
He said: 'Preston North End are a big club with great history and tradition and I am really looking forward to the challenge and opportunity.
'I would like to thank the chairman, owner and board of directors for putting their faith in me and whilst I know the current position is one we do not want to be in, I have every belief in the players' and my own ability to get us out of the situation we are in.
'The supporters of this football club are some of the most knowledgeable in the country and like them I want to see the club progress and I hope to be a part of a successful Preston North End."
Preston have moved quickly to replace Ferguson who was axed after less than a year in charge at Deepdale.
The 38-year-old was shown the exit door with the club rooted to the foot of the npower Championship.
Brown steered Hull to the top flight of English football for thefirst time in their history in 2008, but was sacked lessthan two years later, following the club's slump in form which saw themwin just once in Brown's final 15 games.
Preston set to unveil former Hull manager Brown to replace FergusonBosman XI: Sportsmail selects the team of stars out of contract in the summer
Source: Daily Mail