The 30-year-old, who made the last of his 12 international appearances for the Proteas in 2016, already has county experience after four seasons with Welsh club Glamorgan.
The County Championship will return next year in a group-stage format after it was scrapped this season due to the coronavirus pandemic, the England and Wales Cricket Board said.
The 32-year-old leg-spinner last played the most recent of his 19 Tests in January of last year and he has not featured for Yorkshire in the first-class County Championship during the past two seasons.
English cricket’s domestic calendar will also include the men’s Twenty20 Blast and a 50-over women’s competition.
The fixtures and format for the upcoming English domestic season are to be decided by the 18 First-Class counties in a meeting in July, and plans will be made for both red and white-ball formats.
The England and Wales Cricket Board (ECB) should consider a shortened County Championship season without overseas players for two years to offset the financial impact of the coronavirus outbreak, former England skipper Michael Vaughan said.
Coronavirus Outbreak: Cheteshwar Pujara's short-term deal to play for English county Gloucestershire called off
The 32-year-old Pujara, who has scored 5840 runs at an average of 48.66 in 77 Tests, was supposed to play six County Championship matches for the club at the start of the county's first season back in Division One
Coronavirus Outbreak: Former England captain Nasser Hussain calls for County Championship to be scrapped rather than be a curtailed affair
Former England captain Nasser Hussain feels that ECB should scrap the County Championships this season if the COVID-19 pandemic makes it a really curtailed affair.
Cook believes it is better to call off the championship this season because a shortened campaign would not be meaningful
South Africa vs England: Vernon Philander fined 15 percent match fee for giving abusive send-off to Jos Buttler in farewell match
Philander, playing in his final Test before joining Somerset in the County Championship, was sanctioned for the abusive send-off he gave Jos Buttler after he dismissed the England wicketkeeper on the second day of the fourth and final Test at The Wanderers on Saturday.
Lyon is the latest Australian to sign with an English county for the 2020 season, with Travis Head joining Sussex, Cameron Bancroft at Durham and Peter Siddle returning to Essex
Durham recruited Bancroft, 26, after he had served a nine-month ban imposed for his involvement in the ball-tampering scandal in South Africa that rocked Australian cricket in 2018.
Hampshire's Kyle Abbott takes 17 wickets to register best figures in first-class cricket for 63 years
Kyle Abbott's return of 17-86 against Somerset is the best ever for Hampshire and the best overall since England spinner Jim Laker took 19-90 against Australia in 1956.
England women's cricket team's World Cup-winning coach Mark Robinson resigns after dismal Ashes display
Robinson departs after four years in the role and following a 12 points to four Women’s Ashes series defeat to Australia earlier in the year with England victorious in only one of the seven matches played across all formats.
Ravichandran Ashwin takes five wickets for Nottinghamshire against Somerset in County Championship Division One match
Ravichandran Ashwin returned impressive figures of five for 59 to help Nottinghamshire bowl out Somerset for 169 in their second innings of the County Championship Division One match on Tuesday.
Australia's Cameron Bancroft hits 151 on one-day debut with Durham, says he wants 'to win crowd over'
Cameron Bancroft hit an unbeaten and match-winning 151 on his one-day debut for Durham as the disgraced Australia batsman started to repay the English county's faith in him.
Jason Holder said, "I'm hopeful from a personal point that it will provide me a good opportunity of acclimatising to English conditions and getting some time in the middle ahead of the World Cup in England."
South Africa-born Nick Compton, grandson of England great Denis Compton, played 16 Tests for England, scoring two hundreds.
England all-rounder Sam Curran won the Cricket Writers' Club young cricketer of the year award on Tuesday while his Surrey teammate Rory Burns was named County Championship player of the year.
Uncapped Surrey batsman Rory Burns is set to replace Alastair Cook at the top of England's order after being named in a 16-man squad on Friday for the upcoming three-Test tour of Sri Lanka.