Among those who hailed the Irishman's talent were the trainer Aidan O'Brien and the former champion jockey Frankie Dettori.
Murtagh, 43, spent three seasons as stable jockey to O'Brien's powerful Ballydoyle operation between 2008 and 2010, partnering such greats as Henrythenavigator, Duke Of Marmalade, Dylan Thomas and the incredible Yeats to big-race successes.
O'Brien said: "Johnny was a wonderful rider and we had great years together when he rode for us. He will be a great trainer and we would like to wish him, Orla [Murtagh's wife] and all the family every success in the future."
Murtagh and Dettori enjoyed many thrilling battles down the years. The Italian said: "Johnny is probably one of the best judges of pace I've ever come across and one of the most hard-working and talented jockeys I've ever ridden against.
"I'm genuinely upset that he will no longer be in the weighing room when I go in there."
Murtagh also rode a series of big winners for Eddie Lynam, including Sole Power in the King's Stand Stakes at Royal Ascot last year. The jockey's last ride was on the same horse in the Hong Kong Sprint at Sha Tin in December.
"He's been a great jockey. It's a big loss to me but we'll have to get with it," the County Meath handler said. "I was talking to him on Monday and wished him a happy retirement. He's going to be a good trainer now, so we will have to compete against him.
"He gave Sole Power a fantastic ride in the King's Stand. It was best summed up by James Willoughby that day. He said Johnny sold lengths when they were expensive and bought them when they were cheap. He gave him an extremely good ride that day.
"Murtagh has ridden a lot of big winners for me over the years. He is a top man, a very good jockey and I wish him well in his retirement."
Newmarket trainer Michael Bell teamed up with Murtagh to land the Derby at Epsom in 2005 with Motivator.
"He was a very gifted jockey," Bell said. "I will be forever grateful to him for his input. It was an amazing day when we won the Derby. It was very hard for him to combine both jobs [riding and training], so I'm sure it was the sensible thing to do."
Tony McCoy posted on Twitter: "Best wishes 2@JohnnyMurtagh in his retirement, top bloke, one of the best jockeys I've ever seen & has already proven himself a top trainer."