The purpose of this study is to characterize safety and to determine the putative recommended Phase 2 dose(s) (RP2D[s]), optimal dosing schedule(s) and route(s) of administration of JNJ-80948543 in Part A (Dose Escalation) and to further characterize the safety of JNJ-80948543 at the putative RP2D(s) in Part B (Cohort Expansion).

Inclusion Criteria:

• Histologic documentation of disease: B-cell non-Hodgkin lymphoma (NHL) or chronic lymphocytic leukemia (CLL) requiring therapy.

All participants must have relapsed or refractory disease with no other approved therapies available that would be more appropriate in the investigator's judgment.

B-cell NHL as defined per the 2016 world health organization (WHO) classification. In addition, the following disease-specific criteria outlined below must be met:

If diffuse large B-cell lymphoma (DLBCL) or other high-Grade B-cell lymphoma: Received, or not eligible for high-dose chemotherapy and autologous stem cell transplantation with curative intent or deemed not eligible or fit for an alternative 2nd line therapy. Participants may be eligible if relapsing after chimeric antigen receptors (CAR-T) cell treatment or while waiting for a CAR-T cell treatment.

If transformed lymphoma from low Grade B-cell malignancies: Received or not a candidate for an approved first-line regimen for DLBCL and received or not eligible for high-dose chemotherapy and autologous stem cell transplantation with curative intent.

If follicular lymphoma (FL) (all grades): Previously treated with a minimum of 2 prior lines of systemic therapy, with at least one prior line containing an anti-CD20 antibody.

If mantle cell lymphoma (MCL), marginal zone lymphoma (MZL) (including nodal, extranodal/MALT, and splenic MZL subtypes): Previously treated with at least 2 lines of systemic therapy. H.pylori-positive gastric MALT lymphoma must have failed prior H. pylori eradication therapy as one of their prior lines .

Waldenstrom macroglobulinemia (WM): Previously treated with at least 1 line of systemic therapy.

small lymphocytic lymphoma/chronic lymphocytic leukemia (CLL/SLL): Relapsed or refractory with at least 2 prior lines of therapy, including a Bruton tyrosine kinase inhibitor (BTK) inhibitor or a BCL2 inhibitor, if eligible. In addition for part B Participants must have measurable disease as defined by the appropriate disease response criteria

• Eastern Cooperative Oncology Group (ECOG) performance status Grade of 0 or 1
• Cardiac parameters within the following range: corrected QT interval (QTc intervals corrected using Fridericia's formula [QTcF]) less than or equal to (<=) 480 milliseconds based on the average of triplicate assessments performed no more than 5 (plus minus [+-] 3) minutes apart
• A female participant of childbearing potential must have a negative highly sensitive serum pregnancy test (beta- human chorionic gonadotropin) at screening and must agree to further serum or urine pregnancy tests prior to the first dose, during the study and until 3 months after the last dose of study treatment
• A female participant must agree not to be pregnant, breastfeeding, or planning to become pregnant while enrolled in this study or within 3 months after the last dose of study treatment

Exclusion Criteria:

• Known active central nervous system (CNS) involvement; Lymphoma with CNS involvement may be allowed in pharmacokinetic/ pharmacodynamic (PK/PD) and expansion cohorts if approved by the study evaluation team (SET)
• Prior solid-organ transplantation
• Autoimmune or inflammatory disease requiring systemic steroids or other immunosuppressive agents (example, methotrexate or tacrolimus) within 1 year prior to first dose of study drug
• Toxicity from prior anticancer therapy has not resolved to baseline levels or to Grade <= 1 (except alopecia, vitiligo, peripheral neuropathy, or endocrinopathies that are stable on hormone replacement, which may be Grade 2)
• Clinically significant pulmonary compromise, particularly the need for supplemental oxygen use to maintain adequate oxygenation

The data sharing policy of the Janssen Pharmaceutical Companies of Johnson & Johnson is available at www.janssen.com/clinical-trials/transparency. As noted on this site, requests for access to the study data can be submitted through Yale Open Data Access (YODA) Project site at yoda.yale.edu