The talented second-row was bought from Huddersfield Giants in January initially on a 12-month contract.
He has made 19 appearances since, scoring four tries, and now agreed a contract that takes him through until the end of 2019 at least.
Ferres, 30, joined with Leeds having just completed the ‘treble’ of Super League, Challenge Cup and League Leaders success.
This season, though, has been vastly different with Rhinos at the bottom of the table for much of the campaign only rising to ninth with a late flourish.
They begin life in the Qualifiers – essentially a relegation battle – at Championship club Featherstone Rovers a week on Saturday, live on Sky Sports.
“It is great to get the new deal over the line and know I’ve three great years to come with Leeds,” said Ferres.
“I’ve really enjoyed my time here. Results and our league position have not gone to plan but this is a great club. I’m delighted to be part of it for the next few years. I’ll be looking to knuckle down and make the most of this opportunity to help get the team back to where we want to be at the top of the table.”
The ex-Wakefield Trinity and Castleford Tigers forward added: “The young lads have had a tough experience this year and some of the senior boys have been going through new emotions.
“But I am confident we can come through stronger from the lessons we have learnt together.”
Leeds head coach Brian McDermott said: “Brett has been a very positive influence on our group and I’m delighted he has agreed a new long-term deal.
“I’m sure he’ll benefit from his first season here and be stronger for it next year.
“Our focus now is on the Qualifiers and building on our recent improved performances. I’m sure Brett will be a big part of that.”