Reality tv probably started almost as soon as tv started - back in the late 1940s.

Allen Funt had a Candid Camera tv series that started in 1948.

the first reality tv show was first aired in the 1950s. It featured a band leader and his family. The show actually started on the radio and was a husband and wife affair. The children were brought in and later, after it had transferred to tv, the kids grew up, got married and their wives were also in the show.
It was called The Adventures of Ozzie and Harriet and had its roots in a spot on a radio show in 1935 and lasted 31 years until it ended its tv run in 1966.
Oswald Nelson was born in 1906 in New Jersey. He studied law at Rutgers University and was also a keen musician. To help pay the fees, he was a part-time football coach. He also was in a band, playing saxophone. In time, he learned to play most of the band's instruments.
When the depression hit in late 1929, Oswald realized that there was no guarantee of a job at the end of his studies. He enjoyed playing in the band and as this was a proven source of income, he decided to form his own band and try his luck.
The Ozzie Nelson Band had moderate success playing lowly clubs around New York and the East Coast. When a competition was run by the New York Daily Mirror for readers to vote for their favorite band, he and the band obtained hundreds of unsold newspapers and sent in votes for themselves. When they won the competition the publicity spurred them into a bigger league and they could at least scrape a living. Oswald recruited beautiful 23 year old vaudeville showgirl Harriet Hilliard as lead singer in 1932. They soon fell in love and were married within three years.
Their big break came when they were booked at the Glen Island Casino. Their performance was broadcast on national radio. In those days radio was as big as tv is today and this exposure led to their first big hit And then Some along with regular spots on The Baker's Broadcast radio show from 1935. They were then recruited to do regular spots on another popular radio show, The Red Skelton Show.
In 1936 Harriet gave birth to their first son, David, followed in 1940 by brother Eric, later known as Ricky.
Ozzie and Harriet were increasingly inserting comedy skits between musical numbers, and this seemingly spontaneous repartee went down well with the audience. These were basically skits based around the couple's family life. When Red Skelton was drafted in 1944, Ozzie and Harriet were offered the vacated timeslot and filled it with The Adventures of Ozzie and Harriet. Oswald decided to major on the comedy scripting, with the music taking second place. In time, the music was dropped altogether with the scripts being penned by Oswald. The subject was once again their own family life including their two sons, played by actors.
By 1949 the actors were replaced by the real David and Ricky, largely as a result from pressure from the boys themselves and a guest appearance by Bing Crosby who brought his own two sons along to appear in the show. If Bing's kids could do it, then so could Ozzie's kids.
In 1952 the show was premiered on ABC television. By now David was 16 and Ricky was 12. The theme continued to be the family. Many of the comedy script ideas came from incidents that actually occurred in the Nelson household. If the boys took up a hobby, that would be featured. When David and later Ricky started dating girls this was also included and became a regular theme.
By the time he was 17, Ricky began to take an interest in the new rock 'n' roll music that had taken hold of so many of his generation. He once dated a girl who swooned over Elvis Presley. Not wishing to be outdone, Ricky told her that he was cutting his own disc, a fact that had absolutely no foundation. Wishing to turn this white lie into reality he asked his father to pull some strings. By 1957, Ricky had a recording deal and released Fat's Domino's song I'm Walking. Ozzie duly produced a special script of The Adventures of Ozzie and Harriet that would feature the new song. A few years back this may not have had any great effect, but by the late 1950's television was rapidly being taken up across the country and I'm Walkin' became a big hit. Ricky was an overnight pop idol. Oswald soon realised that the tv show was a perfect way to promote Ricky's records and that the show would attract more viewers, especially teenagers. From this point onwards, Ricky's songs would feature in many of the episodes. When they couldn't be incorporated into the script, a song performance by Ricky would simply be tacked on to the end of an episode.
When the boys finally married - David to June Blair in 1961 and Ricky to Kristin Harmon in 1964 - the art-imitates-life theme was taken to new heights when the wives were cast in the show to play themselves.
Had The Adventures of Ozzie and Harriet not been cancelled in 1966, maybe the show would still be playing with Ozzie and Harriet's grandchildren taking up the baton. What was striking was the way that the scripts, all written or supervised by Oswald, paralleled their real life so closely.
When Ozzie and Harriet cracked their first joke on stage together back in the 1930's, little did they know that this would lead to one of the longest running shows on tv and the grand-daddy of today's reality tv.