Accord Buy-to-Let will now accept product transfer requests and pay brokers a 0.3 per cent procuration fee for retained business.
The lender currently pays brokers a 0.5 per cent fee for new business, which a spokesperson said will be complemented by the new retention payment.
Jeremy Duncombe, director of Accord Mortgages, said the lender was "delighted" to give brokers the option of retaining existing buy-to-let business.
He said: "We understand how important it is to offer intermediaries a procuration fee that reflects their efforts to ensure landlords get a new deal best suited to their needs when their current mortgage deal ends.
"Combined with a new range of deals, we hope brokers feel supported with increased product choices they can offer to those refinancing their portfolio."
The lender has also expanded its range of products available to existing landlords, introducing two, three and five-year deals at 60 per cent, 65 per cent and 75 per cent loan-to-value (LTV) respectively.
Buy-to-let borrowers renewing a portfolio with Accord can access a two-year fixed rate for up to 60 per cent LTV at 2.22 per cent with no completion fee.
A three-year fixed rate for up to 65 per cent LTV at 2.44 per cent with a £950 completion fee is also available, alongside a five-year fix for up to 75 per cent LTV at 2.69 per cent with a £950 completion fee.
Carl Shave, director at Just Mortgage Brokers, said: "Accord's introduction of permitting buy-to-let product transfers from brokers and paying a proc fee of 0.3 per cent is a great addition to their already strong commitment to the intermediary market.
"This now sits nicely within their portfolio of features and products and one that I am sure will be well received by the broker community."