The South Africa-born 23-year-old had been playing club cricket in the East Anglian Premier League this season.
"Sean shows a great maturity with the bat and understands his game well," Kent's high performance director Simon Willis told the club website.
"The number of runs he has scored in all formats is testament to his focus and concentration."
Dickson, who has a British mother and holds a UK passport, has previously played first-class cricket for Northerns in South Africa.
He also bowls medium pace and could make his first-team debut for the club in their T20 Blast match against Glamorgan on Friday.
Kent have not disclosed the length of his contract at the St Lawrence Ground.

Pembroke v Bready
Bready 219-7 (D Rankin 43, J Magee 41)
Pembroke 221-1 (N Cutler 110 no, A Balbirnie 90 no)
Pembroke won by nine wickets
Waringstown v Coleraine
Coleraine 167-7 (D Cooke 71 no)
Waringstown 173-2 (J Hall 91 no, J McCollum 51)
Waringstown won by eight wickets
The Hills v Donemana
Donemana 143 (37.1 overs) (W McClintock 32)
The Hills 144-4
The Hills won by six wickets
Carrickfergus v CIYMS
Carrickfergus 226 (P Botha 63)
CIYMS 229-4 (N Jones 112 no)
CIYMS won by six wickets
Although there is one fixture remaining Muckamore clinched Section A of the Lagan Valley Steels Twenty/20 Cup following a four wicket win over Lisburn. They are undefeated after four games with 20 points while CSNI have 10, Instonians 8 and Lisburn 2. The two Section B games were postponed.
CSNI defeated Instonians by four wickets
Muckamore had a four wicket home win against Lisburn
On Saturday, Challenge Cup holders CSNI were well beaten by CIYMS who join Instonians, Lisburn and Muckamore in the semi-finals.
North-West Cup holders Donemana were 3-2 at one stage but rallied to defeat Coleraine.
The other semi-finalists are Fox Lodge, Bready and Ballyspallen.
CIYMS v CSNI
CSNI 125 (J Kennedy 67)
CIYMS 130-5
CIYMS won by five wickets
Instonians v North Down
Instonians 226 (N Smith 83)
North Down 210
Instonians won by 16 runs
Lisburn v Downpatrick
Lisburn 260 (J Magowan 102, D Simpson 60)
Downpatrick 120
Lisburn won by 140 runs
Woodvale v Muckamore
Muckamore 295-8 (S Gordon 79, J Magowan 74)
Woodvale 122
Muckamore won by 173 runs
Ballyspallen v Strabane
Ballyspallen 191 (G Kennedy 82)
Strabane 158 (A Gillespie 92 not out)
Ballyspallen won by 33 runs
Newbuildings v Bready
Bready 257 (I Samarasooriya 54, D Rankin 51)
Newbuildings 177
Bready won by 80 runs
Ardmore v Fox Lodge
Fox Lodge 221 (S Tshilli 57)
Ardmore 203
Fox Lodge won by 18 runs
Donemana v Coleraine
Donemana 270-9 (W McClintock 125)
Coleraine 220 (D Cooke 41, W McBrine 4-39)
Donemana won by 50 runs

The 25-year-old scored 15 goals in 54 appearances for the U's last season, but has not played a game this term.
The Stags say the deal contains an option to agree a permanent move.
"This is a young man who I first tried to sign when he was scoring goals in the Scottish Premier League for Dundee," manager Steve Evans told the club website.
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Find all the latest football transfers on our dedicated page.
Kent have signed batsman Sean Dickson after he impressed during a trial spell with their Second XI.
[NEXT_CONCEPT]
It was a disastrous afternoon on Sunday for North-West teams as all three lost in the second round of Irish Senior Cup so the quarter-finals will be contested by four from the NCU and four from Leinster.
[NEXT_CONCEPT]
Mansfield Town have signed striker Kane Hemmings from League One club Oxford United on a season-long loan.