The collectibles company has agreed a new licence with HIT Entertainment, which owns the rights.
The relaunch continues a relationship that began 30 years ago when it first developed a Thomas and Friends range.
The models can be ordered now but deliveries will not be made until December.
Hornby said there was still "clear demand" for the Thomas range, which remained the most popular pre-school character in the UK.
Sales have risen by 18% for the year to date, according to market research data from NPD.
A computer animated version of the children's series is shown on Channel 5 and Nickelodeon in the UK, and by broadcasters in many other countries.
A series of events and a feature film later this year are planned to mark Thomas's 70th anniversary. The character was created by Reverend Wilbert Awdry, an Anglican minister.
Richard Ames, chief executive of Hornby, said: "Thomas the Tank Engine has a broad appeal with younger model enthusiasts and importantly, attracts them into the hobby, from which many go on to enjoy both collecting and creating their own model railways.
"We are planning to extend the range of products to support this important market segment."
The company also said that Steve Cooke will join on 10 June as its new finance director, from LSL Property Services.
He will replace Nick Stone, who is leaving in the summer.
Earlier this month Hornby said it expected to make an annual profit for the first time in three years.
The company, which also owns the Airfix and Scalextric model brands, said sales were up by 13% for the year to 31 March.
It expected underlying full-year profits to come in at Â£1.5m.
Shares rose 2.6% to 94.65p in morning trading in London. The stock is up 16% this year, valuing the company at Â£36m.
Hornby, the model toy firm, will relaunch its range of Thomas the Tank Engine railway sets to mark the character's 70th anniversary.