Michael Angelis and Michael Brandon narrated all twenty episodes, but, like Hero of the Rails, voice actors provided the voices for the characters. Mark Moraghan later re-narrated one episode specially for the Santa's Little Engine DVD in 2013.
- Creaky Cranky - Cranky teases Thomas about being small, but when he breaks down it's up to Thomas to save him.
- The Lion of Sodor - Thomas has to deliver The Lion of Sodor to Knapford, but, thinking that it is a real lion, he tries to feed it.
- Tickled Pink - James is sent to the Steamworks to be repainted, but needs to leave suddenly, in a pink undercoat.
- Double Trouble - Thomas takes Sir Topham Hatt to his birthday party, or does he?
- Slippy Sodor - Thomas is teased about his "funny funnel" and causes trouble for Sir Topham Hatt and Mr. Bubbles.
- The Early Bird - While Percy is at the Steamworks for repairs, Thomas must pull the mail, but he doesn't want to ask for his advice.
- Play Time - Charlie, the new engine, challenges Thomas to race him around the Island, causing Thomas to neglect his job.
- Thomas and the Pigs - Thomas is to bring straw to Farmer Trotter's Pig Farm for the piglets who are soon to be born, but Thomas thinks they'll like other things better.
- Time For a Story - After ignoring warning signs about track repair, Thomas' trucks of books derail, so he brings the children to the books.
- Percy's Parcel - After Percy ruins Dowager Hatt's birthday parcel, he hides in a siding. But when he overhears Mavis he gets an idea how to fix his mistake.
- Toby's New Whistle - Toby's bell needs repairs, so he is given a very loud whistle while it's being mended.
- A Blooming Mess - Emily thinks that Mavis needs to be cheered up, so she brings her some flowers, but winds up causing confusion and delay.
- Thomas and the Runaway Kite - After Stephen and Bridget Hatt's kite flies away, Thomas tries to catch it, but realises that he needs to ask for help.
- Steamy Sodor - When Thomas is put in charge of the Steamworks, havoc ensues.
- Splish, Splash, Splosh! - Thomas and Rosie play "Splish, Splash, Splosh", but when Thomas splashes Sir Topham Hatt and Alicia Botti he must put things right.
- The Biggest Present of All - Hiro is visiting Sodor, and the Fat Controller is planning a welcome party for him. Thomas is told to tell the other engines, but looks for a present for Hiro instead.
- Snow Tracks - Gordon is told to not go up any hills, but when he does, he creates a giant snowball.
- Henry's Good Deeds - Henry attempts to help people but ends up scaring away the Sodor Warbler, a very famous bird.
- Buzzy Bees - Thomas' special of bees escape when he goes by a flowery meadow. So he takes Hiro's flower truck to try to lure them back to their hive.
- Hiro Helps Out - Hiro gives the engines orders when he thinks the Fat Controller is too busy to do it himself.
- Sir Topham Hatt
- Lady Hatt
- Dowager Hatt
- Stephen Hatt
- Bridget Hatt
- Farmer McColl
- Alicia Botti
- The Mayor of Sodor
- Farmer Trotter
- The Maithwaite Stationmaster
- The Knapford Stationmaster
- Annie (speaks only in Japanese dub)
- Clarabel (does not speak)
- Henrietta (does not speak)
- Bertie (does not speak)
- The Duke and Duchess of Boxford (do not speak)
- The Tree Specialists (do not speak)
- The Little Engines in the Hills (mentioned)
- Mr. Percival (not named; mentioned)
- Sir Lowham Hatt
- Mr. Bubbles
- Bridget Hatt's friends
- The Bird watcher
- The Mainland Controller (mentioned)
- The Mainland Engines (mentioned)
UK and AUS
- Michael Angelis as the narrator
- Ben Small as Thomas and Toby
- Keith Wickham as Percy, James, Gordon, Henry, Edward, the Fat Controller, Dowager Hatt, Sir Lowham Hatt, the Mayor of Sodor, and Mr. Bubbles
- Teresa Gallagher as Emily, Mavis, Rosie, Lady Hatt, Bridget Hatt and her friends, and the teacher
- Togo Igawa as Hiro
- Matt Wilkinson as Spencer, Rocky, Victor, Kevin, Cranky, Charlie, Stephen Hatt, the Knapford stationmaster, the Maithwaite stationmaster, Farmer Trotter, the bird watcher, and Farmer McColl
- Jules de Jongh as Alicia Botti
- Kerry Shale as Diesel
- Michael Brandon as the narrator, Diesel and Mr. Bubbles
- Mark Moraghan as the narrator (Snow Tracks 2013 only)
- Martin Sherman as Thomas and Percy
- Kerry Shale as Sir Topham Hatt, Henry, Gordon, James, Kevin, Sir Lowham Hatt and the Maithwaite Stationmaster
- William Hope as Edward, Toby, Rocky, Stephen Hatt, Farmer McColl, Farmer Trotter, the Maithwaite Stationmaster (Double Trouble only) and the Knapford stationmaster
- Glenn Wrage as Spencer, Cranky and Charlie
- Jules de Jongh as Emily, Mavis, Rosie, Bridget Hatt and her friends, Alicia Botti, and the teacher
- Togo Igawa as Hiro
- David Bedella as Victor and the Mayor of Sodor
- Keith Wickham as Dowager Hatt
- This is the first season of several things:
- The first season to exclusively use CGI and to use voice actors instead of solely a narrator.
- Sharon Miller's first season as creative producer.
- Marion Edwards' first season as executive producer.
- Greg Tiernan's first season as director.
- Nicole Stinn's first season as producer.
- The first season in which Thomas speaks in every episode.
- This was the second season not to feature the Skarloey Railway and its engines since their introduction, the first being season 8.
- This was the second season in which Thomas appears in every episode, the first one being Season 9.
- Thomas was the main character in thirteen out of twenty episodes, making this the most "Thomas-themed" season.
- This was Dave Peacock's only season as voice director.
- This was Jo Jordan's only season as creative executive.
- From now on all the episodes are eight minutes and fourty-five seconds long, instead of lasting seven minutes.
- The episodes, "Splish, Splash, Splosh!", "Playtime", "Slippy Sodor", and "Snow Tracks" were seen in select US theatres in November 2009.
- "Thomas and the Runaway Kite", "Buzzy Bees", "Toby's New Whistle", and "The Biggest Present of All" were shown in select US theatres in January 2010.
- "The Lion of Sodor", "Thomas and the Pigs", "Time For a Story", and "Hiro Helps Out" were shown in select US theatres in October 2010.
- Thomas' whistle now budges up and down every time he blows it.
- Harold and Trevor also appear in CGI during the Sodor Island intro.
- The Sodor Island intro is not used at the start of individual UK broadcasts from this season onwards.
- Despite being made in 2009, this season was not broadcast until 2010.
- Edward was the only Steam Team member not to get a starring role this season.