Ollie appears at the local allotments and overhears Jean Slater talking about what vegetables she hopes to grow. He introduces himself to her and gives her advice, saying he will keep an eye on her. The next time they meet, he upsets her because she is overwhelmed by his constant talking. He apologises via a note on a fork. They meet again at a speed dating event, and she agrees to see him again. They go on a date but she worries when he says he is a police officer, because she has broken the law. He says he does not care about that and they kiss. Later, she worries he will be put off by the fact she has bipolar disorder, so does not tell him. She does tell him eventually because he thinks she is acting strangely, but she walks away before he can speak. He researches the condition and tells Jean he wants to continue to see her. However, when she cleans instead of getting ready to go out, he says they can go out another night and she thinks he is scared of her bipolar and thinks their relationship is over. He returns a few days later and tells Jean's relative Kat Moon that he made a mistake, but she warns him to stay away. When Jean's friend Shirley Carter prepares to leave, she urges Jean to make up with Ollie. Jean discovers that Ollie has given up his patch at the allotments. She discovers he is retiring to Brighton but is having a party first, so she decides to go, but leaves without seeing Ollie when his friend Frank makes fun of mental illness. The next day, she misses Ollie and is surprised when he arrives to say goodbye. He admits that he loves her and she agrees to come to Brighton with him, but Kat convinces Jean to stay. However, when Kat realises that Jean loves Ollie, she enlists Alfie Moon's help to find Ollie, but they fear they are too late. Ollie finds Jean at the allotments, saying he has cancelled his move so he can stay with her, but she says he cannot stay just for her. They declare their love for one another, and leave for Brighton together with Kat's blessing.
The character and O'Callaghan's casting were announced on 13 June 2013, when it was revealed that Ollie is a gardening enthusiast and a love interest for Jean after she gets her own allotment. O'Callaghan said of his casting, "I am very excited to be joining a show with as much prestige as EastEnders and I'm looking forward to portraying the nice side and humour of Ollie. On 3 June 2014, it was confirmed that O'Callaghan had agreed to reprise his role as Ollie, for a short stint, along with his former co-star, Gillian Wright, who plays his on-screen girlfriend, Jean Slater.