Danny Lomax, played by Stephen Billington, made his first screen appearance on 8th July 2013. Daniel Kilkelly from Digital Spy first mentioned the character in June 2013. He revealed that Danny arrives to teach at Hollyoaks High and becomes a love interest for John Paul McQueen (James Sutton). He added that there are "skeletons in Danny's closet, which could turn the worlds of a number of Hollyoaks residents upside down". Executive producer Bryan Kirkwood added that Danny and John Paul's romance "will lead to dark and unexpected consequences for a number of characters.". On 1 July, Kilkelly announced that Billington had been cast to play Danny and would debut the following week.
A writer from the Hollyoaks website described Danny as "charismatic, charming, pretty-sweeting-captivating". He is also a "thoughtful, intelligent, articulate and well respected member of the teaching profession". Danny is liked by his students because of his youthful approach to life. He also has a "cheeky twinkle in his eyes" which charm everyone. Billington told the writer that can relate to Danny because he also teaches and gets along with young people. But he warned that Danny has a different side to his personality. Viewers will not discover this until later on because it will be revealed over time. Billington added that "you'll still like him, but he’s much more complex than he first appears."
In an unpublicised storyline twist, Danny is revealed to be Ste Hay's (Kieron Richardson) biological father. Billington told Kilkelly that he was "absolutely thrilled" with his storyline and that he was always aware of the development. He explained that Danny had attempted to make contact on many occasions but Ste's mother, Pauline Hay (Jane Hogarth) prevented it. Billington also warned that Danny had more secrets yet to be disclosed and was confident that Danny would be able to charm the audience with his persona. The actor added that Danny is "definitely not a bad person. He's just a bit of a free spirit and he likes getting his own way. Perhaps he's a bit greedy too, but when it comes down to it, he's a fundamentally good guy." The following episode another secret about the character was revealed as viewers were introduced to Danny's wife Sam Lomax (Lizzie Roper). Kilkelly reported Sam would be a prominent character as Danny "desperately" attempts to maintain family life and his affair with John Paul. In September 2013, the show announced the arrival of Danny and Sam's three children Leela (Kirsty-Leigh Porter), Peri (Ruby O'Donnell) and Tegan Lomax (Jessica Ellis).
Danny arrives as a drama supply teacher at Hollyoaks High to organise a production with John Paul. He becomes attracted to Danny and asks him about his sexual preference. He remains secretive and later kisses John Paul. They begin working with Tilly Evans (Lucy Dixon) and Esther Bloom (Jazmine Franks). He goes on a date with John Paul but when he is offered a permanent position at the college, he tells John Paul nothing more can happen between them. Danny changes his mind and arranges a date with John Paul and they sleep together. But once the school holidays begin Danny ignores John Paul's calls. He soon returns to take up his permanent teaching post and successfully pleads for another chance with John Paul. Danny becomes worried when headteacher Patrick Blake (Jeremy Sheffield) mentions that he has acquired job references, he warns Danny not to involve his personal life with his professional role. Tony Hutchinson (Nick Pickard) decides to contact Ste's biological father and he is revealed to be Danny. When John Paul forgets about their date, Danny retaliates by flirting with Ste. They get drunk and go back to Ste's flat. Danny runs off when he finds the birthday card he sent to Ste and Pauline's photograph. John Paul presumes that Danny has slept with Ste and attacks him. Danny denies this and tells John Paul he has a son but does not name Ste. Danny has sex with John Paul before going to meet up with his secret wife Sam. He continues to see John Paul and deceive Sam. His student Robbie Roscoe (Charlie Wernham) discovers their affair and threatens to tell Sam if he does not prevent his expulsion from the college. Doug Carter later figures out that Danny is Ste's dad. Doug confronts Danny and Danny admits to being Ste's dad. At Ste's and Doug's leaving party, a bomb goes off killing Doug. Danny later finds Ste at the deli with a bottle of vodka and pills. Danny tries to stop Ste from committing suicide and Ste tells Danny that he doesn't even know him and that he is nothing to him. Danny then tells Ste that he means everything to him because he is his son.
Of Danny's arrival, a writer from Fabulous magazine said that "there's never a dull moment in Hollyoaks" and quipped that Danny wanted to get involved with John Paul "in more ways than one".