The team finishing bottom of League Two will earn an extra £3,600.
Mr Doncaster admitted that “it has not been the easiest time to go out and sell a title sponsorship”.
He said: “We are well aware of some of the financial issues that have affected some of our member clubs over that period.
“But the reality is that we have had a number of big brands who wanted to partner with us.
“We have had various offers over the period that we’ve rejected, but the clubs’ stance, which we think has been vindicated, was they wanted to wait for the right brand at the right money.”
Ladbrokes chief executive Jim Mullen added: “We love football so we are delighted to be working with the SPFL on one of the best opportunities in British sport.
“This partnership will help to propel Ladbrokes and the SPFL to new heights and will put us at the heart of Scottish football throughout the year. Getting people engaged with great sport and making sure they share our passion is at the very core of everything we are about.”
Ladbrokes has more than 2,100 shops across the UK and has recently sponsored rugby league’s Challenge Cup, extended its backing of horse racing’s St Leger Festival at Doncaster and continues to sponsor The Ladbrokes World Hurdle at the Cheltenham Festival.