Matching placebo will be administered as subcutaneous injection.

DAPSA assessed the joint domain of psoriatic arthritis (PsA) and was derived from the sum of the following components: tender joint count (0-68), swollen joint count (0-66), CRP level (milligram/deciliter [mg/dL], value less than [<] lower limit of quantification [LLOQ] is considered equal to half of the value of LLOQ for numerical calculations), participant assessment of pain (0-10 cm VAS, 0=no pain, 10=worst possible pain), and participant's global assessment of disease activity on arthritis (0 to 10 cm VAS, 0=excellent and 10=poor). A higher score indicates more active disease activity. Negative changes from baseline indicate improvement of PsA disease activity. The assessment does not have a score range with an upper or lower bound.

HAQ-DI score assess functional status of participant. It is 20 question instrument that assess degree of difficulty a person has in accomplishing tasks in 8 functional areas (dressing, arising, eating, walking, hygiene, reaching, gripping, and activities of daily living). Responses in each functional area were scored from 0=indicating no difficulty, to 3=indicating inability to perform a task in that area. Total HAQ score is average of the computed categories scores ranging from 0-3 where 0=least difficulty and 3=extreme difficulty. Lower scores are indicative of better functioning. Negative change from baseline indicates improvement of physical function.

Percentage of participants with IGA 0/1 response at week 24 among the participants with >= 3 percent (%) BSA psoriatic involvement and an IGA score of >= 2 (mild) at baseline will be reported. The IGA documents the investigator's assessment of the participants psoriasis at a given timepoint. Overall lesions are graded for induration, erythema, and scaling using 0 (no evidence), 1 (minimal), 2 (mild), 3 (moderate) and 4 (severe) scale. The IGA score of psoriasis is based upon the average of induration, erythema and scaling scores. The participant's psoriasis is assessed as cleared (0), minimal (1), mild (2), moderate (3), or severe (4).

Change from baseline in SPARCC score for MRI SI joints at week 24 among the participants with a positive MRI of the sacroiliac joints at baseline will be reported. SPARCC method focuses on the cartilaginous portion of the SI joint, and scores presence (score of 1) versus absence (score of 0) of bone marrow edema in each SI joint quadrant.

Percentage of participants who achieve a >= 50 % improvement from baseline in BASDAI score at week 24 will be reported.

Percentage of participants who achieve ASDAS clinically important improvement at week 24 will be reported.

Percentage of participants who achieve ASAS 40 response at Week 24 will be reported. ASAS 40 defined as improvement from baseline of >= 40% and with an absolute improvement from baseline of at least 2 on 0 to 10 cm scale in at least 3 of following 4 domains: Participant's global assessment (0 to 10 cm; 0=very well, 10=very poor), total back pain (0 to 10 cm; 0=no pain,10=most severe pain), BASFI (self-assessment represented as mean (0 to 10 cm; 0=easy to 10=impossible) of 10 questions, 8 of which relate to participant's functional anatomy and 2 relate to participant's ability to cope with everyday life), Inflammation (0 to 10 cm; 0=none, 10=very severe); no worsening at all from baseline in remaining domain.

Percentage of participants who achieve ASDAS major improvement at Week 24 will be reported.

Change from baseline in SPARCC score for MRI spine at week 24 among the participants with a positive MRI of the spine at baseline will be reported. The SPARCC scoring system for the spine scores the 6 discovertebral units considered by the reader as the most abnormal, and then separately assesses each quadrant of 3 adjacent sagittal slices, with additional points for "depth" and high "intensity" of the lesion.

An AE is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the pharmaceutical/biological agent under study.

A SAE is any untoward medical occurrence that at any dose: results in death; is life-threatening; requires inpatient hospitalization or prolongation of existing hospitalization; results in persistent or significant disability/incapacity; is a congenital anomaly/birth defect; is a suspected transmission of any infectious agent via a medicinal product; is medically important.

An AE is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the pharmaceutical/biological agent under study.

Number of participants with AEs leading to discontinuation of study intervention will be reported.

Number of participants with infections will be reported.

Number of participants with injection-site reactions will be reported. A study intervention injection-site reaction is any adverse reaction at a subcutaneous study intervention injection-site.

Number of participants with laboratory abnormalities (chemistry, hematology) by maximum toxicity (CTCAE 5.0) grades will be reported. Grade refers to the severity of the AE as follows: Grade 1- Mild, asymptomatic or mild symptoms, clinical or diagnostic observations only, intervention not indicated; Grade 2- Moderate, minimal, local or noninvasive intervention indicated, limiting age-appropriate instrumental Activities of Daily Living (ADL); Grade 3- Severe or medically significant but not immediately life-threatening, hospitalization or prolongation of hospitalization indicated, disabling, limiting self-care ADL; Grade 4- Life-threatening consequences, urgent intervention indicated; Grade 5- Death related to AE.

Serum guselkumab concentration over time will be reported.

Number of participants with antibodies to guselkumab will be reported.