Keith is something of a 'couch potato', who loves to sit around watching documentaries. He has his own chair with the television remote stuck around it with tape. He was originally claiming incapacity benefits due to a back injury, but they were withdrawn after Stacey Slater caught him on CCTV in the Minute Mart moving heavy boxes and reported him for benefit fraud. He has since fought hard to remain unemployed and is presumably claiming Jobseeker's Allowance.
It was later discovered that he can't read or write, but he is now learning fast with the encouragement of his family.
Keith and Rosie are not actually married, despite her hints, but they call each other husband and wife. Keith left Rosie in January 2006 after he discovered she was planning to leave him for her ex-husband, Mike Swann, and went to live with Garry Hobbs and Minty Peterson. He later forgave Rosie when she begged for another chance and moved back in with her. Mike then left the Square, but later left a message on the Millers' answerphone for Dawn, with his new mobile number. Keith deleted the message as he didn't want Mike to have anything to do with the family. Mike's mother, Nora Swann, later died in hospital and they had no way of contacting Mike to let him know. Rosie then kicked Keith out of the house and he went to live with Gus and Juley Smith. Keith desperately wanted Rosie back and knew the only thing he could offer her was marriage. Keith proposed, and he and Rosie got back together. Since then, Keith tried his best to put things off, as he was not really interested in getting married. He later realised that nothing would really change after they got married, and soon changed his mind.
Rosie didn't want to put off the wedding any longer, and the wedding ceremony took place on 4 July 2006 at Walford Register Office. However, Keith turned up late with mud on his suit. Rosie couldn't go through with the wedding and jilted Keith halfway through the ceremony. Rosie spent the night at The Queen Victoria. Keith then decided he could change his ways and help out more around the house. However, this was not going to change Rosie's mind. She told Keith she had fallen out of love with him, and wanted to take a job out in the Cotswolds, and take Darren, Demi and Aleesha with her. On 7 July she prepared to leave with the children. Darren did not want to go, but Rosie convinced Keith to make Darren leave, by saying he was not interested in his son. Darren was upset and decided to go. On their way out of Walford, Rosie could see how upset Darren was and decided to tell him the truth: that Keith had made it up. Rosie then allowed Darren to stay in Walford with Keith.
In 2007 Keith told Darren he had got another flat in Streatham. After Darren slept in the Square. Keith decided it was best to stay in Walford.
Also in 2007 after Dawn came back after nearly being killed by May, Keith was furious and snapped at Rob. When Dawn left and gave birth on her way to Rosie's house, Keith kept Rob at his house and tortured him by pouring gravy all over him and letting Genghis lick it off.
On 13 November, a gang led by Terry Bates were out to hunt for Jase Dyer for revenge. They invaded the Vic to see if he was there, only to find out that Jase was with Dawn. As Keith was about to escape to warn Jase, one of Terry's gangmembers beat him down to the ground until he was knocked out.
On 2nd June 2008, he won the lottery. However he later discovered he had lost the ticket due to a hole in his jacket pocket. The next day Dawn, Mickey and Darren were all furious at Keith for losing the ticket. To make peace Keith offered to get a job, however as he was talking to Bianca Jackson on the bus, he became nervous and decided to back out of going to the Job Centre and later lied to Dawn about his appointment. Having gotten the new position as roadsweep by the council, Bianca come along and informed Dawn that Keith bottled out of his job centre appointment. After this, Dawn, Mickey and Darren threw Keith out of the house.
On 5 June, after spending the night on Arthur's bench, Keith called in a favour from Masood Ahmed (whose family had previously stayed with him) and moved into the Masoods much to the chagrin of Zainab.
On 19th June, Dr. May Wright, set the house on fire. Keith, who was supposed to be on the lookout for May, instead was in the Queen Vic revising for a pub quiz with Masood. In shock after witnessing the explosion, and wracked with guilt for not helping Dawn, wrapped himself in the British flag and went into the burning house and successfully rescued Dawn. Despite suffering from smoke inhalation they both made a full recovery. Keith and the Masoods were now joined by the rest of the Miller clan, along with Dawn's fiance Jase and his son Jay, while Number 27 was being refurbished.
On 1st July 2008, Mickey discovered a letter from Rosie offering Keith a job working as a concierge at the hotel she was working at in the Cotswolds. Keith, however, had kept this letter hidden from the rest of the family for over a month. Angry that he had not followed up to contact Rosie about the job, Mickey applied for the job instead. Standing outside the boarded up number 27, Keith admitted to Dawn that he still loved Rosie but couldn't take the risk of accepting the job and being rejected by her. As Mickey was all set to leave following the pub quiz a newly groomed Keith, along with Genghis, entered the Vic and told Mickey he had decided to accept the job after all and that he was coming with him.
After an emotional send-off from the regulars in the Vic; Keith, Mickey and Genghis headed off to start a new life in the Cotswolds.
On August 22, It was mentioned by Dawn to Darren that Keith and Rosie were in the midst of a reconciliation.
It was further revealed on 6 October by Dawn, that Keith and Rosie have reconciled