The 54-year-old has agreed to join the Bees at least the end of the season and steps in to the role vacated by Mark Warburton after he took over as manager.
Warburton on Tuesday was appointed to replace Uwe Rosler after the German left for Championship side Wigan at the weekend.
McParland had been director of Academy and head of player development at Liverpool until last month.
He had previously worked at Anfield as chief scout from 2003 to 2007 and held roles at Bolton and Watford before returning to Liverpool in 2009.
Brentford chairman Cliff Brown told the club website: "Frank has a fantastic background, working for one of the top clubs in the country.
"He is an expert in player recruitment and development, believes passionately - as we do - in bringing players through the Academy to the first team and has some superb contacts.
"Mark Warburton knows Frank well and we are happy they can work together.
"The important thing for us when appointing a new management team was continuity, building on all that has been achieved this season and in the past two and a half years. We believe Frank can help us do that."