Mauricio Pochettino expects to be at Southampton next season and is looking forward to working with chairman Ralph Krueger.
Loan pair Sam Hutchinson and Leon Best have extended their deals at Sheffield Wednesday.
The 28-year-old will complete the temporary switch to Tannadice subject to international clearance.
The forward won a move to Brentford last summer after netting 28 goals in the Scottish First Division with Falkirk.
United boss Jackie McNamara said: "This is the ideal time for us to bring in Farid.
"He scores goals, has strong aerial ability and will hold the ball up and allow his fellow attackers to get involved.
"We have moved quickly to secure him because there was interest from other clubs and I am delighted to sign him.
"He will bring something a little different from what we have at the club and will enhance our attacking threat."